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  • 101
    Electronic Resource
    Electronic Resource
    A Variable-Pressure 2D 1H-NMR Study of the Mechanism of Trimethyl Phosphate Intermolecular Exchange and cis/trains-Isomerisation of Tetrachlorobis(trimethyl phosphate)zirconium(IV)Part 45 of the series ‘High-Pressure NMR Kinetics’; for part 44, see[1]. (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 199-202 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In chloroform, [ZrCl4·2(MeO)3PO] exists in both cis- and trans-isomeric forms. Three reactions can be envisaged in the presence of excess (MeO)3PO = L: (1) cis-[ZrCl4·2L] + *L⇆cis-[ZrCl4·L*L]+ L; (2) trans-[ZrCl4·2L] + *L ⇆ trans-[ZrCl4·L*L] + L; (3) cis-[ZrCl4·2L]⇆ trans-[ZrCl4·2L]. To distinguish between these possible reaction pathways, we have used 2D 1H-NMR spectroscopy. For the first time, variable-pressure 2D exchange spectra were used for mechanistic assignments. cis/trans-Isomerisation was found to be the fastest reaction (in CHCl3/CDCl3), with a small acceleration at higher pressure: it is concluded to be an intramolecular process with a slightly contracted six-coordinate transition state. The intermolecular (MeO)3PO exchange on the cis- and trans-isomer are second-order processes and are strongly accelerated by increased pressure: Ia mechanisms are suggested without ruling out limiting A mechanisms.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19900730123
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  • 102
    Electronic Resource
    Electronic Resource
    Catalysis of Ion Transfer by Tetraphenylborates in Neutral Carrier-Based Ion-Selective Electrodes (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 203-212 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: For certain ionophores of extremely high lipophilicity, kinetic limitations of the carrier-induced ion transfer between aqueous and membrane phase may heavily disturb the electromotive behaviour of the ion-selective membrane electrode. These limitations may be overcome by adding tetraphenylborates to the membrane phase. Membranes prepared with different 3,6-dioxaoctanediamide homologues and potassium tetrakis(P-chlorophenyl)borate as phase-transfer catalyst all exhibit the same ion selectivity as well as theoretical electrode response. This behaviour is corroborated by a theoretical description of the ion-transfer process.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19900730124
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  • 103
    Electronic Resource
    Electronic Resource
    Blockcopolymers in microemulsions differential heats of solution and shift of the percolation temperature in W/O microemulsions (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 213-220 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Solutions of blockcopolymers (POE-b-PI-b-POE) in fluids of interacting aqueous nanodroplets (W/O microemulsions) are studied. The interaction strength between the (pseudo) two components is measured by the shift of the percolation temperature relative to that of the pure microemulsion. A quantitative measure of the interaction, the differential heat of solution, is thermodynamically related to the slopes of the equilibrium temperature of the system with varying monomeric nanodroplet concentration and the experimental percolation line in the presence of copolymer.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19900730125
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  • 104
    Electronic Resource
    Electronic Resource
    Mitteilungen (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 229-232 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19900730127
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  • 105
    Electronic Resource
    Electronic Resource
    Synthese cyclischer Depsipeptide durch direkte Amid-Cyclisierung: 12gliedrige Depsipeptide mit alternierender Sequenz von α-Hydroxy- und α-Aminosäuren (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 221-228 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Synthesis of Cyclic Depsipeptides via Direct Amide Cyclization: Cyclic Depsipeptides with 12-Ring Atoms and Alternating Sequence of α-Hydroxy and α-Amino AddsThe reaction of 3-(dimethylamino)-2,2-dimethyl-2H-azirine (1; R1 = R2 = R3 = R4 = Me) with α-hydroxy-carboxylic acids, followed by selective hydrolysis of the terminal dimethylamide group yields the dipeptide analogues 15a and 18b (Schemes 3 and 4). After protection of the OH group (→ 16a and 19, resp.), coupling with the C-terminus-protected derivatives 14 and 18a, respectively, by a modified 1,1′-carbonyldiimidazole procedure followed by hydrolysis gives the linear depsipeptides 17c and 20, respectively. Treatment with HCl gas in toluene at 100° leads to the cyclic depsipeptides 21 and 22 in very good yield. The two model reactions show that the ‘azirine/oxazolone-method’, combined with the ‘direct amide cyclization’, is a versatile procedure for the synthesis of cyclic depsipeptides containing α,α-disubstituted α-amino acids.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19900730126
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  • 106
    Electronic Resource
    Electronic Resource
    Masthead (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990) 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19900730201
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  • 107
    Electronic Resource
    Electronic Resource
    A Study on the Odour/Structure Relationship of Patchoulol and NorpatchoulenolPresented in part at the ‘11th Congress of Essential Oils, Fragrances and Flavours’, New Delhi, 12-16th November, 1989. (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 1730-1733 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In continuation of studying structure/activity relationships of odorous compounds, the influence of the bridgehead-bonded Me group of (+)-norpatchoulenol (1) and (-)-patchoulol (2) and the olfactory properties of the corresponding unsaturated and saturated derivatives (±)-3, (±)-4 and (±)-5, (±)-6, respectively, are studied. The key odour descriptors-wood, earth, and camphor-are used for classification.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19900730618
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  • 108
    Electronic Resource
    Electronic Resource
    Synthesis of the 6-C-Methyl and 6-C-(Hydroxymethyl) Analogues of N-Acetylneuraminic Acid and of N-Acetyl-2,3-didehydro-2-deoxyneuraminic Acid (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 1742-1763 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of 6-C-methyl-Neu2en5Ac (4), 6-C-(hydroxymethyl)-Neu2en5Ac (5), and 6-C-methyl-Neu5Ac (6) is described. The 4-methylumbellyferyl glycosides 8 and 9 were also prepared but proved unstable. Protection of the previously reported nitro ether 10 (→11) followed by a Kornblum reaction gave the branched-chain derivative 13 which was transformed into aldehyde 14 and hence via 16 into the-protected 6-C-hydroxymethylated 20 and into the 6-C-methyl-substituted 18 (Scheme 1). Debenzylidenation of 20 and 18 afforded the diols 21 and 19, respectively. Selective oxydation of 19 followed by esterification (→ 22), acetylation (→ 23), and elimination led to the protected 6-C-methyl-Neu2en5Ac derivative 24 (Scheme 2). Bromomethoxylation yielded mainly 25 and some 26, which were reductively debrominated to 27 and 28, respectively. Attempted deprotection of 27 did not lead to the corresponding acid, but to the 2,7- and 2,8-anhydro compounds 29 and 30 which were characterised as their peracetylated esters 31 and 32 (Scheme 3). The structure of 32 was established by X-ray analysis. Oxydation of 19 and 21, followed by deprotection, esterification, and acetylation gave 37 and 38, respectively (Scheme 4). The branched-chain Neu2en5Ac derivatives 4 and 5 were obtained by β-elimination (→ 39 and 40) and deprotection. Omission of the esterification after oxydation of 33 and 34 gave the lactones 35 and 36 which were transformed into 37 and 38, respectively. Bromoacetoxylation of 39 gave 41-43 which were reductively debrominated to 44 (from 41 and 42) and 45 (Scheme 5). Bromoacetoxylation of 40 yielded 46 which was debrominated to 47. Glycosidation of the glycosyl chlorides obtained from 44 and 47 led to the α -D-glycosides 48 and 49 and to the elimination products 39 and 40, respectively (Scheme 6). Transesterification of 48, followed by saponification gave the unstable glycoside 8 and hence 6-C-methyl-Neu5Ac (6). The unstable glycoside 9 was obtained by similar treatment of 49 but yielded 50 under acidic conditions. The branched-chain 4 and 5 were weak inhibitors of Vibrio cholera sialidase, and 8 and 9 were very poor substrates.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19900730620
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  • 109
    Electronic Resource
    Electronic Resource
    Conversion of Light into Electricity with Trinuclear Ruthenium Complexes Adsorbed on Textured TiO2 Films (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 1788-1803 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A series of CN-bridged trinuclear Ru complexes of the general structure [RuL2(μ-(CN)Ru(CN)L2′)2] where L is 2,2′-bipyridine-4,4′-dicarboxylic acid and L′ is 2,2′-bipyridine (1)2,2′-bipyridine-4,4′-dicarboxylic acid (2), 4,4′-dimethyl-2,2′-bipyridine (3), 4,4′-diphenyl-2,2′-bipyridine (4), 1,10-phenanthroline (5), and bathophenanthrolinedisulfonic acid (6) have been synthesized, and their spectral and electrochemical properties investigated. The two carboxylic functions on the 2,2′-bipyridine ligand L serve as interlocking groups through which the dye is attached at the surface of TiO2 films having a specific surface texture. The role of these interlocking groups is to provide strong electronic coupling between the π* orbital of the 2,2′-bipyridine and the 3d-wave-function manifold of the conduction band of the TiO2, allowing the charge injection to proceed at quantum yields close to 100 %. The charge injection and recombination dynamics have been studied with colloidal TiO2, using laser photolysis technique in conjunction with time-resolved optical spectroscopy. Photocurrent action spectra obtained from photo-electrochemical experiments with these trinuclear complexes cover a very broad range in the visible, making them attractive candidates for solar light harvesting. Monochromatic incident photon-to-current conversion efficiencies are strikingly high exceeding 80% in some cases. Performance characteristics of regenerative cells operating with these trinuclear complexes and ethanolic triiodide/iodide redox electrolyte have been investigated. Optimal results were obtained with complex 1 which gave a fill factor of 75 % and a power conversion efficiency of 11.3% at 520 nm.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19900730624
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  • 110
    Electronic Resource
    Electronic Resource
    A Novel Type of Dimeric Secoiridoid Glycoside from Lisianthius jefensis ROBYNSet ELIAS (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 1845-1852 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A dimeric secoiridoid glucoside named lisianthioside (l) has been isolated from the roots of Lisianthius jefensis ROBYNS et ELIAS (Gentianaceae). The structure was established by spectroscopic analysis (UV, IR, 1H- and 13C-NMR, DCI-MS) of glycoside 1, peracetate 1a, aglycone 3 and the dimethoxy derivatives 4a-c. Lisianthioside (1) is the first representative of a novel type of dimeric secoiridoids. Biogenetically derived from two sweroside (2) moieties, the tricyclic aglycone features a symmetrical 12-membered bislactone ring. In contrast to the moderately bitter sweroside (2), lisianthioside (1) is tasteless.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19900730706
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  • 111
    Electronic Resource
    Electronic Resource
    2,4-Disubstituted Pyrrolo[2,3-d]pyrimidine α-D- and β-D-Ribofuranosides Related to 7-Deazaguanosine (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 1879-1887 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Nucleobase-anion glycosylation (KOH, tris[2-(2-methoxyethoxy)ethyl]amine (TDA-1), MeCN) of the pyrrolo[2,3-d]pyrimidines 4a-d with 5-O-[(1,1-dimethylethyl)dimethylsilyl]-2,3-O-(1-methylethylidene)-α-D-ribo-furanosyl chloride (5) gave the protected β-D-nucleosides 6a-d stereoselectively (Scheme 1). Contrary, the β-D-halogenose 8 yielded the corresponding α-D-nucleosides (9a and 9b) apart from minor amounts of the β-D-anomers. The deprotected nucleosides 10a and 11a were converted into 4-substituted 2-aminopyrrolo[2,3-d]-pyrimidine β-D-ribofuranosides 1. 10c, 12, 14, and 16 and into their α-D-anomers, respectively (Scheme 2). From the reaction of 4b with 5, the glycosylation product 7 was isolated, containing two nucleobase moieties.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19900730710
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  • 112
    Electronic Resource
    Electronic Resource
    Reaktionen von 5H-1,2λ5-Azaphospholen mit Arylazocarbonitrilen sowie Acetylendicarbonsäure-esternHerrn Prof. Dr. Gerhard Pfleiderer zum 70. Geburtstag gewidmet (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 1888-1893 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reactions of 5H,2λ5-Azaphospholes with Arylazocarbonitriles and Dialkyl AcetylenedicarboxylatesAzaphospholes 1a-c react with activated arylazocarbonitriles to 1,5,2λ5-diazaphosphorines 2a-c and 3a-c. The reaction of 1a-c with diethyl or dimethyl acetylenedicarboxyiates yields 7H-1,4λ5-azaphosphepines 4a-c. The structures of 2b, 3a, and 4a are established by an X-ray diffraction analysis.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19900730711
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  • 113
    Electronic Resource
    Electronic Resource
    Cycloalkylations of N-(ω-Halogenoalkyl)-substituted Macrocyclic Imides (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 272-276 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: With ω-halogenoalkyl isocyanates, 2-oxocyclododecane-l-carbonitrile is transformed under ring enlargement to 1-(ω-halogenoalkyl)-2,14-dioxo-1-azacyclotetradecane-3-carbonitriles. In the presence of base, these products undergo O- or C-alkylation leading to bicyclic compounds. The C-alkylation product 7 undergoes solvolysis to form a sixteen-membered ring compound.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19900730205
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  • 114
    Electronic Resource
    Electronic Resource
    Design and Synthesis of Novel Opiate Antagonists with LH-Stimulating Properties (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 326-336 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Opiate antagonists stimulate the release of LH and might, therefore, contribute to an innovative therapy for the treatment of numerous clinical syndromes characterized by hypofunction of the HHG axis. The purpose of this work was to design and synthesize pure opiate antagonists useful for this therapy. Me, Et, Pr, and PhCH2 groups were introduced at the crucial 14β-position of morphines and morphinans via a hetero-Diels-Alder key step starting from thebaine derivative 1 and tested for opiate antagonism and LH-stimulating activity. Me-, Et-, and Pr-substituted compounds 11a-c were stronger antagonists than naltrexone, whereas Pr and PhCH2 substituents in 11c, 11d, 9d, 9d3, 9d4, and 9d5 led to orally active LH stimulators. Based on our finding that the μ-antagonists 12 and 11b5 showed no LH stimulation, we conclude that a combination of both μ-and χ-antagonism is necessary for potent LH stimulation.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19900730212
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  • 115
    Electronic Resource
    Electronic Resource
    Dehydration of Alkanones by Bare FeO+ Involves the ω/(ω - 1) Positions: Exclusion of Iron Carbenes as Intermediates. Preliminary Communication (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 380-385 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Fourier-transform ion-cyclotron-resonance (FTICR) mass spectrometry has been used to uncover the mechanisms by which FeO+ dehydrates heptan-4-one (5a) and nonan-5-one (6a) in the gas phase. The study of isotopomeric ketones provides evidence that H2O loss is not due to a 1,1-elimination, thus ruling out the intermediacy of high-valent iron-carbene species. Rather, H2O is generated in a formal 1,2-elimination involving the ω/ω - 1 positions of the alkyl chain (‘remote C—H bond activation’). In the consecutive alkene/H2O elimination, the olefins (ethylene from 5a and propene from 6a) originate from the terminal part of one alkyl chain, and the H-atom is transferred to the FeO+ moiety in the course of this process, builds up together with an H-atom from the ω/ω-1 position of the other alkyl chain the H2O molecule. In either case, the O-atom of H2O is provided by the FeO+ species.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19900730217
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  • 116
    Electronic Resource
    Electronic Resource
    trans-Disubstituted Cyclohexadienes via Sequential Addition of a Carbon Nucleophile and an Electrophile to (η6-Benzene)tricarbonylchromium: Scope of Carbon Electrophiles (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 386-404 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A regio- and stereoselective route from benzene to trans-disubstituted cyclohexadienes via complexation of the arene to the tricarbonylchromium group is reported. The key step involves an alkylation/carbonylation sequence of the anionic tricarbonyl (η5-cyclohexadienyl)chromium complex (3) which is readily obtained by the addition of 2-lithio-2-methyldithiane (2) to (η6-benzene)tricarbonylchromium (1; cf. Scheme 6). In situ reaction of 3 with alkyl halides (in THF, THF/HMPA, THF/DMPU), followed by oxidation (I2, Ce(IV)) or ligand exchange (CO, Ph3P, Et3N) produced, with complete stereo- and regioselectivity, trans-5,6-disubstituted cyclohexadienes (15 examples). The cyclohexadiene substituent originating from the alkyl halide in all cases is an acyl group which shows that CO insertion into the metal-alkyl bond precedes reductive elimination to form the cyclohexadiene product. When, in the reaction of 3 with Mel, NHS3 was used to induce carbonylation und decornplexation, the isomerized, conjugated 1,4-cyclohexadiene 13 was obtained almost exclusively. The electrophile selectivity in the reactions with 3 is consistent with a nucleophilic, SN2-like mechanism with a high preference for primary iodides. Chloride, ketone, and ester functions in the electrophile are unreactive and are tolerated; a primary alkyl iodide reacted selectively in the presence of a secondary iodide. In one case, the trans-configuration in a cyclohexadiene product 7 was demonstrated by the Diels-Alder reaction with maleic anhydride. High facial selectivity was observed in this reaction giving a single diastereoisomer resulting from endo-addition of the dienophile to the diene face carrying the acyl group. The anionic intermediate 3 was trapped with Ph3SnCl, and an X-ray analysis of the resulting cyclohexadienyl [Cr(CO)3(R)] complex 15 provides evidence for electrophile addition to the metal. In the solid state, the Ph3Sn group in 15 is trans-configurated to the dithianyl substituent. The ready access to [Cr(arene)(CO)3] complexes, the high selectivity of the reactions reported here and the mild decomplexation provide rapid access to Cyclohexadienes that possess functionality and are attractive for further transformation.
    Additional Material: 5 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19900730218
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  • 117
    Electronic Resource
    Electronic Resource
    Structure Determination of a New Spirobicyclic Triterpenoid from Iris foetidissimaDedicated to Professor André Pirson, co-founder of today's botany, on the occasion of his 80th birthday (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 433-438 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The novel iridal 10 has been isolated from rhizome extracts of Iris foetidissima. Its structure was established by spectroscopic methods and oxidative degradation. Final proof of the spirobicyclic nature of the compound - a new feature in the triterpenoid field - was afforded by the correlations observed in the 2D-HMBC- (1H-detected multiple-bond heteronuclear multiple-quantum coherence) spectrum. The possible biogenesis of this unusual compound is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19900730223
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  • 118
    Electronic Resource
    Electronic Resource
    Diastereoselective Spirocyclization of C-(Alkyloxycarbonyl)formimines of 2-Substituted 1HIndole-3-ethanamines (= Tryptamines): Basic Studies. 5th Communication on Indoles, Indolenines, and Indolines4th communication: [1]. (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 439-454 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: C-(Alkoxycarbonyl)formimines of type 15-18 were derived from the 2-substituted tryptamines 2, 9, 10, and 11 and transformed with tosyl chloride into tricyclic 3-spiroindoles of types 19-22 (Scheme 3). The influence of the homochiral alkoxy moieties A-D on the stereochemical outcome of this reaction was studied. Good-to-excellent diastereoselectivities were observed with the (-)-8-(phenylmenth-3-yl)oxy group (B) as homochiral auxiliary. The structures of the tricycles 4, (2′R,3S)-19B, and (2′S,3R)20C were established by X-ray analysis, the structures of the others by NOE and CD studies, and by chemical correlation. Possibilities to explain the steric course of the spirocyclizations are discussed.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19900730224
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  • 119
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    Further Studies on the Biosynthesis of Tabtoxin (Wildfire Toxin): Incorporation of [2,3-13C2]Pyruvate into the β-Lactam Moiety (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 476-482 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: [2,3-13C2]Pyruvic acid (7) was synthesized and administered to cultures of Pseudomonas syringae pv tabaci. C(2) and C(3) of 7 were incorporated as an intact unit into the β-lactam moiety of tabtoxin (1). The result suggests that the biosynthesis of 1 is proceeding in part along the lysine pathway. The labelling pattern in 1 and an incorporation experiment with α,α′-dideuterated (±)-2,6-diaminopimelic acid (19) indicate that the branching in the biosynthesis of 1 occurs before lysine is formed.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19900730228
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  • 120
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    Masthead (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990) 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19900730301
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  • 121
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    A CD-Spectroscopic Alternative to Methylation Analysis of Oligosaccharides: Reference Spectra for Identification of Chromophoric Glycopyranoside Derivatives (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 509-551 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A microscale method for identifying the monosaccharide units and their linkages in oligosaccharides is presented. Sugar components are identified by UV and CD spectroscopy of chromophoric degradation products. CD spectral data for approximately 150 different glycopyranoside components are provided for use as reference spectra in the identification of unknown derivatives. Procedures for the conversion of oligosaccharides to monosaccharide subunits bearing 4-bromobenzoate and 4-methoxycinnamate chromophores have been developed based on acetolysis/bromination reactions for glycosidic cleavage of per (bromobenzoylated) oligosaccharides. The method offers an alternative means to conventional methylation analysis of oligosaccharides.
    Additional Material: 24 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19900730302
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  • 122
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    Herstellung von ‘Semialdehyd’-Derivaten von Asparaginsäure- und Glutaminsäure durch Rosenmund-Reduktion (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 405-410 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Preparation of ‘Semialdehyde’ Derivatives of Aspartic and Glutamic Acid via the Rosenmund ReductionSuitably protected aspartic-acid ‘β-semialdehyde’ and glutamic-acid ‘γ-aldehyde’ derivatives can be obtained, in good yield by Rosenmund reduction of the corresponding acid chlorides. Benzyloxycarbonyl (Z) and (tert-butoxy)carbonyl (Boc) protecting groups are not affected under these reaction conditions. The sensitive aldehydes, which are obtained in higher purity than by hydride reductions, can directly be used for further transformations like aldol-type reactions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19900730219
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  • 123
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    Mammalian Alkaloids: O-Methylation of (±)-Norcoclaurine-1-carboxylic Acid and Related Isoquinolines Including (S)- and (R)-Norcoclaurine with 14C-Labeled S-Adenosyl-L-Methionine in Presence of Mammalian Catechol O-Methyltransferase (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 426-432 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: (±)-Norcoclaurine-1-carboxylic acid (5) and the derived dihydroisoquinolinone 6 (present as quinonemethide 6a at pH 7) afforded, on methylation with 14C-labeled S-adenosyl-L-methionine in the presence of mammalian catechol O-methyltransferase, exclusively the 7-O-methylated congeners 7 and 9, respectively. High stereoselectivity of the O-methylation was observed with (-)-(S)- and (+)-(R)-norcoclaurine (2a and 2b, resp.), affording 80% of 6-O-methylated isoquinoline 12 and 20% of the 7-O-methylated isomer 11 from 2a, and the reversed proportion of 12 and 11 from 2b. Synthesis of the reference amino acid 8 was achieved by Pictet-Spengler condensation of O-benzyl-protected dopamine 17 with benzyl-protected keto acid 20 (→ 21) followed by methylation with diazomethane (→22 + 23) and removal of the protecting groups by acid hydrolysis. It is considered unlikely that amino acids such as 5 constitute important precursors in the biosynthesis of isoquinolines related to reticuline.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19900730222
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  • 124
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    2H-benzimidazoles. Part 5Part 4: [1].. Convenient synthons for tricyclic heterocyclesDedicated to Salo Gronowitz on the occasion of his 65th birthday (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 902-911 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The readily available 5-nitrospiro[2H-benzimidazole-2,1′-cyclohexane] (1) was converted into the carbonitrile 5 and the 4-phenylthio derivative 4. The NO2 or the PhS substituents in 4 could be replaced regiospecifically by reaction with Me3SiN3 or NaN3, respectively. The 5-azido derivative 8, resulting from NO2-group replacement was made to cyclize photolytically to give the angular spiro[cyclohexane-imidazophenothiazine] 18. The azide 9 obtained from the PhS replacement in 4 cyclized spontaneously to give the angular spiro[cyclohexane-imidazobenzoxadiazole] 10 which, on reductive hydrolysis, furnished benzofurazan-4,5-diamine 14. The diamine 14 was converted by conventional methods into a imidazobenzoxadiazole 15, oxadiazoioquinoxaline 16, and selenadiazoloxadiazole 17. The carbonitrile 5 was converted, in simple steps, into the ‘stretched-out’, angular pteridine and purine analogues, 25 and 28, respectively.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19900730417
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  • 125
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    Photochemical reactions. 152nd Communication151st communication: [1].. Photochemistry of acylsilanes; photolysis and thermolysis of cyclopropyl silyl ketonesDedicated to Prof. Dr. H. R. Christen on the occasion of his 65th birthday (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 922-931 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The photolysis and thermolysis of the Cyclopropyl silyl ketones 3, 4, and 5 are described. On n,π* excitation, the silyl ketones 3 and 4 undergo a Norrish-type-II reaction involving γ-H abstraction, cyclopropyl ring cleavage followed by retro-enolization to the acylsilanes 6 and (E/Z)-12, respectively. As a common product of 3 and 4, the dihydrofuran 7 is formed via the alternative C(α)-C(β) cleavage of the cyclopropyl moiety. Compounds 6, 7, and (E/Z)-12 are new types of acylsilane photoproducts. The irradiation of acylsilane 5 gave the analogous dihydrofuran 15 as the only product. On photolysis of 3 and 4, products 8A + B and 13A + B, derived from a siloxy carbene intermediate, were found as well. On thermolysis of 3 and 4, the acylsilanes 6 (80%), and (E)-12 (33%) and (Z)-12 (34%), respectively, are formed as the only products. Their formation may occur via a [1, 5] sigmatropic H-shift. The thermolysis of 5 gave the diene 16 whose formation can be explained by insertion of a siloxycarbene into the neighboring cyclopropane leading to the cyclobutene 28 as thermally unstable intermediate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19900730420
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  • 126
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    Konstitutionsisomerie in Polykondensaten. Teil VITeil V: [1].. Synthese und Eigenschaften von völlig geordneten und ungeordneten Bipolyamiden aus cis-2,6-Dimethylpiperazin und 1,2,5-Thiadiazol-3,4-dicarbonyl-dichlorid (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 839-855 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Constitutional Isomerism in Polycondensates. Synthesis and Properties of Perfectly Regular and Random Bipolyamides from cis-2,6-Dimethylpiperazine and 1,2,5-Thiadiazole-3,4-dicarbonyl DichlorideThe synthesis of constitutionally perfectly regular and random alternating copolyamides from the ‘symmetric’ monomer 1,2,5-thiadiazol-3,4-dicarbonyl dichloride (4) and the ‘non-symmetric’ monomer cis-2,6-dimethylpiper-azine (7) by solution and interfacial polycondensation methods is described. Their constitutional regularities (s values) were determined by high-resolution 13C-NMR spectroscopy in CDCl3 solutions. Ordered and random copolyamides were amorphous with Tg values of ca. 200°. However, the regular head/tail and the random copolyamides with low molecular weights could be partially crystallized by annealing and showed large differences in their melting points (54°). Beside other physical properties, the membrane properties of the copolyamides were carefully investigated. In H2O desalination by reverse osmosis, no differences in salt rejections and permeabilities between constitutionally regular and random copolyamides were found (within experimental errors). In contrast, the regular head/head/tail/tail- and head/tail-type copolyamides showed considerably larger separation factors in the gas separation (methane/hydrogen) than the random ones.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19900730409
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  • 127
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    Technical Procedures for the Syntheses of Carotenoids and Related Compounds from 6-Oxo-isophorone: Syntheses of (3R,3′R)-Zeaxanthin. Part IIDedicated to Dr. Otto Isler on the occasion of his 80th birthday (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 868-873 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Starting from the readily available, optically active (4R)-hydroxy-2,2,6-trimethylcyclohexanone (2), a new technical synthesis of (3R,3′R)-zeaxanthin is described. According to a completely new C9+C2+C4 = C15 scheme, the ketone 2 was protected, ethynylated with Li-acetylide, and the C11-intermediate 6 was acetylated, followed by dehydration. The product 10 was protected, deprotonated, and subsequently reacted with methyl vinyl ketone to provide the C15-propargylate 13. Reduction in situ of 13 with Vitride yielded the olefinic C15-alcohol 11 which was transformed into the known C15-Wittig salt 3. A double Wittig reaction of this salt with the C10-dialdehyde 4 afforded nature-identical zeaxanthin (1).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19900730412
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  • 128
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    Photorearrangement of 4,4-Dimethylcyclohex-2-enones with Alkyl or Fluoro Substituents at C(5) and C(6): In Search of the Mechanism (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 890-895 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The photorearrangement of cyclohex-2-enones 4a-h to bicyclo[3.1.0]hexan-2-ones 5 and cyclopent-2-enones 6 (λ = 350 nm, MeCN) was investigated. Both the quantum yield (Φ-4 = 0.004- 0.024) and the product ratio (5/6 = 65:35-31:69) vary only over a rather small range, indicating the rearrangement to be relatively insensitive to substituents on C(5) or C(6). Compounds 4b, 4c, and 4g with just one alkyl group at either C(6) or C(5) rearrange selectively to the diastereoisomer 5 with alkyl group and three-membered ring in trans-configuration, while 6-fluorocyclohex-2-enones 4d and 4f afford mixtures of diastereoisomeric bicyclohexanones. Mechanistic conclusions regarding an intermediate trimethylene biradical are presented.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19900730415
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  • 129
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    The Syntheses of Purine and Pyrimidine Secoribo-nucleosides: Acyclo-uridine Derivative of Cyclophosphamide (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 912-915 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of secoribo-nucleoside analogues is described. Compounds 4 and 5 possess interesting antiviral effects in vitro. A procedure is also developed for the conversion of acyclo-uridine nucleoside 7 to a novel derivative of cyclophosphamide 8.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19900730418
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  • 130
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    Synthesis of rel-(3RS,3aSR,7aSR)-3-(4-Chlorophenyl)-3a,4,5,6,7,7a-hexahydro-1-methylindolin-6-one, the Main Metabolite of the Analgesic Ro 15-8081: A Potent Amine-Uptake InhibitorDedicated to Dr. O. Isler on the occasion of his 80th birthday (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 932-939 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of the title compound 2 and its diastereoisomer 3 was accomplished using tricarbonyl[1-5-n-(4-methoxycyclohexa-2,4-dien-1-yl)]iron tetrafluoroborate (4) as a precursor to the cyclohexanone ring. The assignments of the relative configurations of 2 and 3 are based on the X-ray analysis of compound 3. Both compounds 2 and 3 are potent inhibitors of neuronal noradrenaline uptake in rats with similar potencies in vitro as compared to amitriptyline and desipramine. Compounds 2 and 3 are less potent as serotonin-uptake inhibitors, very weak inhibitors of dopamine uptake, and virtually devoid of antinociceptive activity.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19900730421
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  • 131
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    The synthesis of DL-1-(hexadecanoyloxy)methyl- and 1-O-hexadecanoyl-inositols as potential inhibitors of phospholipase CDedicated to Dr. O. Isler on the occasion of his 80th birthday (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 1037-1057 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of racemic analogues of phosphatidylinositol (PI) and phosphatidylinositol 4,5-bisphosphate (PIP2) starting from myo-inositol is described. Inositol derivatives with and without homologalion at C(l) and with and without ionic groups (phosphate or sulfate) at C(4) and C(5) were prepared as well as homologated derivatives with deoxy composition at C(2) and/or C(6). In all these compounds, palmitate ester groups were introduced in place of the diacylglyceryl group of PI or PIP2.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19900730428
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  • 132
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    Die Synthese des Labdanditerpenes Erigerol und analoger VerbindungenHerrn Dr. Otto Isler zum 80. Geburtstag gewidmet (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 1108-1138 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The Synthesis of the Labdane Diterpenoid Erigerol and of Analogous CompoundsThe synthesis of Erigerol (1) and of analogous compounds in a 23-step sequence is described. The various difficulties of the synthesis and several blind alleys that have been followed are discussed.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19900730433
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  • 133
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    Mitteilungen (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 1148-1148 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19900730435
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  • 134
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    Highly Regioselective Nitration of Hexamethylbenzene and Its Derivatives to Dinitroprehnitene with Excess Nitronium TetrafluoroborateAromatic substitutions, Part 61. Part 60:[1] (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 1167-1170 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Hexamethylbenzene and its derivatives undergo very clean regioselective dinitration to dinitroprehnitene (1, 2, 3, 4-tetramethyl-5, 6-dinitrobenzene) with excess of nitronium tetrafluoroborate in dry CH2C12 solution. The mechanism of this unexpected new nitration is also discussed.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19900730504
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  • 135
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    Eine weitere, diesmal erfolgreiche Suche nach 3′-Epilutein in Pflanzen11. Mitt. über Rosenfarbstoffe; 10.Mitt., s.[1]. (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 1205-1209 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A Further, Now Successful Search for 3′-Epilutein in PlantsThe 3′-epilutein, an extremely rare carotenoid, found till now in only one plant, was detected in anthers of flowers of several roses and in those of peonies.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19900730508
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  • 136
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    Synthesis and Chemical Transformations of 4, 5-Homosnoutene Derivatives: An Attempted New Access onto the (CH)12 Energy Hypersurface (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 1182-1196 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Pentacyclo[6. 4. 02, 4. 03, 10. 07, 9]dodeca-5, 11-diene(4) is proposed as new potential precursor of the truncated tetrahedrane 1. The synthesis of several new pentacyclo[5. 4. 0. 02, 4. 03, 9. 06, 8] undec-10-ene (4, 5-homosnoutene) derivatives including homosnouten-5-one(10), 5-methylidenehomosnoutene(19a) as well as homosnoutene-5-carb-aldehyde(17b) and their reactions directed toward ring enlargement to the skeleton of 4 are reported. Although all the homosnoutenes resisted ring expansions, several unexpected new polycyclic systems were obtained. Any intermediate developing a cationic center at C(5) of the skeleton of 10 rearranged with release of strain and opening of one or both three-membered rings to give compounds such as 22 and 23. The aminomethyl derivatives 13a and 13b, upon diazotation, underwent a remarkable fragmentation to give 10 and homosnouten-5-o1(20), respectively. The 5-(dibromomethyl) homosnouten-5-o1(14), upon treatement with t-BuLi, rearranged to the pentacyclic ether 15, while the carbine 11b, generated by the thermal or photochemical decomposition of the tosylhydrazone salt of 17c, solely gave 19a by C, H insertion. The 1, 1-dicyclopropylethene unit in 19c was excited selectively upon irradiation, but the products 26 and 27 of this photochemical rearrangement were derived only from n-participation in diradical intermediates 25a-25c.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19900730506
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  • 137
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    The Reactivity of the Pentacyano(η1-Dioxygen)cobaltate(III) Ion in Aqueous Solution (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 1219-1227 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The mononuclear η1-dioxygen complex [Co(CN)5O2]3- (A) decomposes in aqueous solution to the hydroxo-complex [Co(CN)5OH]3- (B) and the hydroperoxo complex [Co(CN)5CoO2N]3 (C). The mechanism involves partial dissociation of A to give [Co(CN)5]3- (E) which binds with unreacted A to give the η1:η1-peroxo complex [(CN)5Co02Co(CN)5]6- (F) which is hydrolysed to B and C. The mechanism is supported by the effects of pH, dioxygen concentration, and ionic strength on the rate of decomposition, and by the trapping of oxidation products of E and F. Complex A reacts readily with reducing agents to give directly the hydroperoxo complex C.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19900730511
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  • 138
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    Determination of the Chemical Structure of Linden Ether (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 1250-1257 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The chemical structure of the novel monoterpene 1, named ‘linden ether’ and isolated from linden honey and the blossoms of lime tree (Tilia cordata), was studied by two-dimensional NMR spectroscopy, by high-resolution MS as well as by hydrogenation experiments and by GC on a chiral phase. Thus, linden ether was identified as a racemic mixture, i.e. (7aRS)-2, 4, 5, 7a-tetrahydro-3, 6-dimethylbenzofuran.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19900730515
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  • 139
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    Rh(II)-Catalyzed Isomerizations of Cyclopropenes Evidence for Rh(II)-Complexed Vinylcarbene Intermediates (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 1233-1241 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The thermocatalytic rearrangements of cyclopropenes 1-4 have been investigated in the presence of Rh(IT) perfiuorobutyrate. 1, 2, 3-Triphenylcyclopropene (1a) undergoes rearrangement lo diphenylindene 5a or, with alkoxycyclopropene derivatives, to α, β-unsaturated ketone 6. Furan formation occurs with 2, 3-diphenylcyclo-propenecarboxylate 2, but the diethyl counterpart 3 rearranges to dienoate 8. 2-Alkylcyclopropenecarboxylates 4 afforded (E)-methylidenecyclopentane derivatives 9 as the only isolable product in yields of ca. 35 %. A mechanism involving regio- and stereospecific cyclopropene ring opening to a Rh-complexed vinylcarbene and insertion of the latter into the C—H bond to give 9 is proposed. An analogous mechanism should account for the rearrangement products of 1 to 3.
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    Synthesis of Optically Active Bifunctional Isoprenoid Building Blocks by Rhodium(I)-Catalyzed Asymmetric Allylamine to Enamine IsomerizationPresented in part at the ‘6th International Symposium on Homogeneous Catalysis’, Vancouver, Canada, August 21-26, 1998.Dedicated to Dr. Otto Isler on the occasion of his 80th birthday (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 1258-1275 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The application of the known asymmetric allylamine to enamine isomerization methodology to bifunctional C5-isoprenoid allylic amines of types IId and IIe (Scheme 1) is described. It is shown that a number of such substrates can be isomerized with enantioselectivities of 〉 90% ee. using cationie Rh1 complexes containing (6. 6′-dimethylbiphenyl′2, 2′-diyl)bis(dipheny phosphine) (BIPHEMP; 9) as asymmetry-inducing ligand (Scheme 2, Tables 1 and 2). Synthetically most useful is the isomerization of the benzyloxy derivative 10a into the (E)-enamine 11a. This isomerization proceeds with very high enantioselectivity (98-99% ee) and affords, after enamine hydrolysis, the optically active 4-(benzyloxy)-3-methylbutanals ((R)- or (S)-12) in chemical yields of ca. 90%. In conjunction, a short synthetic route to the starting material 10a has been developed which has a Pd-catalyzed amination of isoprene epoxide (30) as the key step. Thus, convenient and practical access to the optically active aldehydes (R)-and (S)-12 is now at hand. These aldehydes are useful optically active bifunctional building blocks for isoprenoid homologation.
    Additional Material: 2 Tab.
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  • 141
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    Synthesis of All Four Stereoisomers of (E)-Vitamin KT (Phylloquinone), Analysis of Their Diastereoisomeric and Enantiomeric Purities and Determination of Their BiopotenciesPresented in part at the ‘6th International Symposium on Homogeneous Catalysis’, Vancouver, Canada, August 21-26, 1988.Dedicated to Dr. Otto Isler on the occasion of his 80th birthday (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 1276-1299 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: All four stereoisomers of (E)-vitamin Kb i. e. (21E, 7R, 111R)-l (= 1a), (21E, 71 R, l11S)-1 (= 1b), (21E, 71 S, 111S) 1 ( = 1c), and (21E, 71S, 111R)-l ( = Id), have been synthesized in a state of high chemical and stereoisomeric purity. The synthesis of stereoisomers lb-d relied on the use of the optically active Cf1* and C*10-building blocks (R)- or (S)-4-(benzyloxy)-3-methylbutanal ((R)- or (S)-2) and (R)- or (S)-citronellal ((R)- or (S)-3) which had been secured by the Rh1-catalyzed allylamine-to-enamine isomerization technology. For the synthesis of the natural (E)-vitamin-K1 stereoisomer 1a, a new route starting from natural phylol was developed, based on an O-alkylation/rearrangement procedure. A HPLC method was developed which separates with remarkable efficiency all four stereoisomers of (E)- as well as three out of the four stereoisomers of (Z)-vitamin K1 on optically active poly(trityl methacrylate) as the chiral stationary phase supported on Nucleosil. By this method, the stereoisomeric content of the stereoisomers 1b-d synthesized was shown to be in the range of 96-98 %, while the natural isomer 1a was configurationally uniform. The biological activity of the four (E)-vitamin-K1 stereoisomers was determined by means of the curative prothrombin time test with vitamin-K-depleted chicks. A high precision of the results was obtained with the recently introduced up-and-down organization of the test and the statistical evaluation according to an estimation procedure. With the natural (E)-vitamin-K1 stereoisomer 1a as standard (set at 1. 0), activities of 0. 93, 1. 19, and 0. 99 were found for stereoisomers 1b, 1c, and 1d, respectively. Within the confidence limits, these activity ratios can be regarded as identical, A very similar efficacy was obtained by comparison of (E, all-rac )-vitamin K1 ((21E, RS, 11′ RS)-1; equimolar mixture of the four stereoisomers 1a-d) with the natural (E)-vitamin-K1 stereoisomer 1a). A synergistic effect was not detectable, as was the case with the eight α-tocopheryl-acetate stereoisomers.
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  • 142
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    Synthesis of Pyrrolidine Analogues of N-Acetylneuraminic Acid as Potential Sialidase Inhibitors (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 1338-1358 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The pyrrolidine derivatives 3, 4, and 5 were prepared from the methyl ester 7 of Neu2en5Ac via lie pyrrolidine-borane adduct 33. They inhibit Vibrio cholerae sialidase competitively with Ki = 4. 4 10-3 M, 5. 3 10-3 M, and 4. 0 10-2 M, respectively. Benzylation of 7 gave the fully O-benzylated 8 besides 9, 10, and 11. Ozonolysis and reduction with NaBH4 of 8 and 9 gave the 1, 4-diols 12 and 15, the hydroxy acetates 13 and 16, and the furanoses 14 and 17 (Scheme 1), respectively. The diol 12 was selectively protected (→19→20→23) and transformed into the azide 27 by a Mitsunobu reaction. Selective base-catalysed deprotection of the diacetate 22, obtained from 12, was hampered by an easy acetyl-group migration. The mesylate 28 proved unstable. The azide 27 was transformed via 29 into the ketone 30 (Scheme 2). Hydrogenation of 30 gave the dihydropyrrole 31 and, hence, the pyrrole 32. The adduct 33 was obtained from 30 by a Staudinger reaction (→31) and reduction with LiBH4/HBF4. It was transformed into the pyrroudine 34. The structure of 34 was established by X-ray analysis. Reductamination of the pyrrolidine-borane adduct with glyoxylic acid gave 40 and, hence, 3. N-Alkylation afforded 44 and, hence, the phosphonate 4. The acid 5 was obtained from 33 by acylation (→47) and deprotection (Scheme 4).
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  • 143
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    Chemie von α-Aminonitrilen3. Mitteilung über die Chemie von α-Aminonitrile. 2. Mitteilung:[1]. Aziridin-2-carbonitril, ein Vorläufer von rca-O3-Phosphoserinnitril und Glycolaldehyd-phosphat (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 1391-1409 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Chemistry of α-Aminonitriles. Aziridine-2-carbonitrile, a Source of Racemic O′-Phosphoserinenitrile and Glycolaldehyde PhosphateRacemic aziridine-2-carbonitrile (rac-1) in MeCN solution reacts regioselectively (〉 90%) with 2 equiv. of TsOH at room temperature to form the hydrotosylate of racemic O3-tosylserinenitrile (rac-2) via β-ring opening (Scheme 2). A similar regioselective reaction takes place between rac-l and H3PO4 to produce racemic O3-phosphoserinenitrite (rac-3) which is in turn a source of glycolaldehyde phosphate (=formylmethyl dihydrogenphosphate) under the conditions of a ‘retro-Strecker’ reaction in aqueous solution (Scheme 6). These experiments document a close structural relationship between the simplest of the sugar phosphates and an α-aminonitrile precursor. The English Footnotes (*) referring to Schemes 1-7 are intended to provide an extension of this summary.
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  • 144
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    Chemie von a-Aminonitrilen4. Mitteilung über die Chemie von α-Aminonitrilen. 3. Mitteilung:[1]. Aldomerisierung von Glycolaldehyd-phosphat zu racemischen Hexose-2,4,6-triphosphaten und (in Gegenwart von Formaldehyd) racemischen Pentose-2,4-diphosphaten: rac-Allose-2,4,6-triphosphat und rac-Ribose-2,4-diphosphat sind die Reaktionshauptprodukte (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 1410-1468 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Chemistry of α-Aminonitriles. Aldomerisation of Glycolaldehyde Phosphate to rac-Hexose 2,4,6-Triphosphates and (in Presence of Formaldehyde) rac-Pentose 2,4-Diphosphates: rac-Allose 2,4,6-Triphosphate and rac-Ribose 2,4-Diphosphate Are the Main Reaction ProductsGlyclaldehyde phosphate aldomerizes in aqueous NaOH solution to a product mixture containing the racemates of the two diastereoisomeric tetrose 2,4-diphosphates and eight hexose 2,4,6-triphosphates. At room temperature in the absence of air and after 7 days, a solution 0.08Min glycolaldehyde phosphate (=formylmethyl dihydrogenphosphate)and 2M in NaOH gives products, in up to 80% yield, with a tetrose/hexose derivative ratio of ca 1:10 and with rac-allose, 2,4,6-triphosphate comprising up to 50% of the mixture of sugar phosphates. When the reaction is run under the same conditions but in the presence of 0.5 mol-equiv. of formaldehyde, sugar phosphates are formed in up to 45% yield, with pentose 2,4-diphosphates now predominating over hexose triphosphates by a ration f 3:1 rac-Ribose 2,4-diphosphate is found to be the major component, the ratios am ribose, arabinose, lyxose, and xylose 2,4-diphosphates being 52:14:23:11 in a representative experiment. The pentose diphosphates are constitutionally stable under the reaction conditions (observed for 23 weeks), but the diastereoisomeric ratios slowly change with time (tc 22:34:30:14 after 23 weeks), showing that ribose 2,4-diphosphate is not the thermodynamically favored diastereoisomer. The observed product distributions in both the pentose and the hexose series (after 1 week) reveal an aldolization mode that is preferentially erythro in the product-determining step (the reaction of glycolaldehyde phosphate as its enolate with glycerinaldehyde 2-phosphate and tetrose 2,4-diphosphate, respectively). An attempt is made to rationalize both this fact and the kinetic predominance of ribose 2,4-diphosphate in the pentose series and allose 2,4,6-triphosphate in the hexose series. Their configuration along the C-chain can be interpreted as corresponding to a minimum number of 1-5 repulsions in the packing of phosphate and OH substituents and minimal steric interaction between substituents at the reaction centers in the transition state of the product-determining step. The aldomerization of glycolaldehyde phosphate in the presence of formaldehyde is a variant of the formose reaction, It avoids the formation of complex formose product mixtures, largely as a consequence of the fact that aldoses which are phosphorylated at the C(2)
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  • 145
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    The crystal structure of [1.1.1]propellane at 138 K (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 1574-1585 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The molecular structure of [1.1.1]propellane has been determined from single-crystal X-ray diffraction measurements at 138 K. The crystals of this reactive compound were grown from the melt at ca. 263 K. The space group is C2, and the asymmetric unit contains four molecules. All have large thermal motion and two show orientational disorder as well. Because of these problems, the atomic positions cannot be determined with high accuracy. Within the experimental limits, the two ordered molecules have D3h symmetry, with corrected lengths of central and side bonds of ca. 1.60 Å and 1.53 Å, respectively. At lower temperature, the crystals undergo a phase transition. The transition temperature, in the range of 100 to 132 K, varied from one crystal sample to another. All crystals obtained of the low-temperature phase were twinned, and its space group could not be established.
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    URL: http://dx.doi.org/10.1002/hlca.19900730603
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  • 146
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    Long-Range Intramolecular Electron Transfer between two Naphthalene π-Moieties Attached to a Rigid Norbornylogous Spacer of Variable Length: An ESR and ENDOR Study (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 1586-1601 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ESR, ENDOR, and TRIPLE-resonance studies are reported on the radical anions of 7(1,0), 7(2,0), and 7(1,1) in which a completely rigid spacer separates two naphthalene π-moieties by 2, 4, and 6 C—C single bonds, respectively. Whereas 7(1,0)\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\scriptstyle {{\relbar}\kern-4pt {.} }} $\end{document} has to be considered as a ‘truly’ charge- and spin-delocalized radical anion of a homobinaphthylene-like system, the frequency of intramolecular electron transfer in 7(2,0)\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\scriptstyle {{\relbar}\kern-4pt {.} }} $\end{document} and 7(1,1)\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\scriptstyle {{\relbar}\kern-4pt {.} }} $\end{document} is governed by the migration rate of the counterfort (K+) between two equivalent sites at the π-moieties. Under conditions of tight ion pairing (solvent 2-methyltetrahydrofuran), the unpaired electron in 7(2,0)\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\scriptstyle {{\relbar}\kern-4pt {.} }} $\end{document} and 7(1,1)\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\scriptstyle {{\relbar}\kern-4pt {.} }} $\end{document} is localized on one π-moiety and the pertinent spectra resemble that of the radical anion produced from an analogous mononaphthalene derivative 8. On the other hand, with solvents of higher cation-solvating power (1,2-dimethoxyethane or its mixtures with N,N,N′,N′,N″,N′-hexamethylphosphoric triamide), delocalization of the electron spin over both π-moieties becomes evident, thus indicating that the electron-transfer rate exceeds the hyperfine time-scale (ca. 107s-1). Simultaneous occurrence of ‘localized’ and ‘delocalized’ radical anions is also observed, in particular for 7(1,1)\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\scriptstyle {{\relbar}\kern-4pt {.} }} $\end{document}. Previous findings for the radical anion of 6(1) which, like 7(1,1)\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\scriptstyle {{\relbar}\kern-4pt {.} }} $\end{document}, contains two naphthalene π-moieties separated by 6 C—C single bonds are reinterpreted in the light of the results obtained in the present work. Exhaustive reduction of 7(2,0) and 7(1,1) leads to the formation of triplet dianions in which each of the two π-moieties houses one unpaired electron.
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  • 147
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    Neoflor und 6-Epineoflor aus Blüten von Trollius europaeus; Hochfeld-1H-NMR-Spektren von Neoxanthin und (9′Z)-Neoxanthin (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 1637-1643 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Neoflor and 6-Epineoflor from Flowers of Trollius europaeus; Highfield 1H-NMR Spectra of (all-E)-Neoxanthin and (9′Z)-NeoxanthinRe-isolation of the very polar carotenoids from flowers of the title plant furnished two epimeric pentahydroxy compounds. Based on spectroscopical and chiroptical arguments and by chemical correlation with neoxanthin, their structures were established as 11 (proposed name neoflor) and 12 (6-epineoflor), Decoupling experiments and COSY-2D-1H-NMR spectra allowed a complete assignement of the vinyl protons of the two isomers, and furthermore, for the first time, also of those of (all-E)-neoxanthin and (9′Z)-neoxanthin.
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    URL: http://dx.doi.org/10.1002/hlca.19900730608
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  • 148
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    Reduktive Co-Alkylierung von Heptamethyl-cobyrinat mit dem Methylthiomalonat (S)-Methyl-3-bromo-2-[(ethylthio) carbonyl]-2-methylpropanoatHerrn Prof. Dr. Albert Eschenmoser zum 65. Geburtstag gewidmet (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 1659-1668 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reductive Co Alkylation of Heptamethyl Cobyrinate with the Methylthiomalonate (S)-Methyl 3-Bromo-2-[(ethylthio)carbonyl]-2-methylpropanoateThe methylthiomalonate(-)-(S)-Methyl 3-bromo-2-[(ethylthio)carbonyl]-2-methylpropanoate(5a)was prepared from dimethyl methylmalonate in five steps via the stereospecific cleavage of the (pro-S)-ester group of 1 with pig-liver esterase in an overall yield of 26.5% (Scheme 4a). Reductive Co alkylation of heptamethyl Coβ-perchlorato cob (II)yrinate (8) with 5a by electrosynthesis lead to the alkylcobalt complex 9a in 40% yield (Scheme 4b). The O2-dependent reactions of the methyhnalonyl fragment produced by photolysis of 9a and its deuterated derivative 9c are reported (Scheme 5).
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    URL: http://dx.doi.org/10.1002/hlca.19900730611
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    Mitteilungen (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 1804-1805 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19900730625
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  • 150
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    Reinvestigation of the Conformation of Cyclosporin A in Chloroform (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 1818-1832 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: New investigations of cyclosporin A in CDCl3 have been performed to obtain additional and more accurate distance restraints than utilized in our previous studies of cyclosporin A. Build-up rates at 600 MHz using 6 different mixing times at low temperatures (252.5 K) were determined and transformed into distances using the two-spin approximation. With the new distance restraints in the MD simulations using the GROMOS package, we can unambiguously conclude the presence of a βII′-turn. The new structure resembles the X-ray structure more than the structure previously determined, especially regarding the orientation of the MeBmt side chain. In the new structure and in the solid state, the side chain is folded over the backbone (although there are substantial differences in the χ1 torsion), in contrast to the old structure, where the side chain is extended away from the backbone.
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  • 151
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    Synthèse énantiospécifique du (+)-(6S, 8R, E)-2,3-didéhydrononactate de méthyle (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 1861-1864 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Enantiospecific Synthesis of (+)-(6S,8R,E)-Methyl 2,3-Didebydrononactate(+)-(6S,8R,E)-Methyl 2,3-didehydrononactate (7) has been synthesised from (-)-(3R)-methyl 3-hydroxy-butanoate with an enantiomeric excess ≥95%. The known stereoselective hydrogenation of 7 affords (-)-(2R,3R,6S,8R)-methyl nonactate (8) as the major isomer, a chiral synthon for the synthesis of nonactin.
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    Synthesis of 2-Acetamido-2-deoxy-D-gluconhydroximolactone- and Chitobionhydroximolactone-Derived N-Phenylcarbamates, Potential Inhibitors of β-N-Acetylglucosaminidase (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 1918-1922 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The N-phenylcarbamate 7, derived from 2-acetamido-2-deoxy-D-gluconhydroximo-1,5-lactone (3) and the analogous N-phenylcarbamate 14, derived from chitobionhydroximo-1,5-lactone (10) have been prepared as potential inhibitors of β-N-acetylglucosaminidases. The unambiguous synthesis of the hydroximo-1,5-lactone 3 involves oxidation of the oxime 1, followed by deprotection with Na/NH3.
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    URL: http://dx.doi.org/10.1002/hlca.19900730714
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  • 153
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    Synthese von Pyrano[3,2-b][1]benzopyranen aus 1-Nitroglycalen (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 1923-1930 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Synthesis of Pyranol [3,2-b][1]benzopyrans from 1-NitroglycalsA synthesis of pyrano[3,2-b][l]benzopyrans β-addition of salicylic aldehyde to 1-nitroglycals, followed by a Henry reaction, is described. This sequence gave the cis-annelated pyranobenzopyranes 9 and 11 from 5 in 54 and 9% yield, respectively, demonstrating the pronounced diastereoselectivity of the β-addition. Reductive denitration of the crude product mixture yielded 14(75%), 15(15%), and 16(7%), which were oxidized to the aryl ketones 20 and 21, respectively. Reduction of 20 (NaBH4) gave exclusively 15. The ketone 20 was deprotected to 22 and 23.
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    URL: http://dx.doi.org/10.1002/hlca.19900730715
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    Carotinoide mit 7-Oxabicyclo[2.2.1]heptyl-Endgruppen. Teil I. Versuch einer Synthese von Cycloviolaxanthin (= (3S,5R,6R,3′S,5′R,6′R)-3,6:3′,6′-Diepoxy-5,6,5′,6′-tetrahydro-β,β-carotin-5,5′-diol) (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 1954-1969 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Carotenoids with 7-Oxabicyclo[2,2.1]heptyl End Groups. Attempted Synthesis of Cycloviolaxanthin ( = (3S,5R,6S,3′S,5′R,6′R)-3,6:3′,6′- Diepoxy-5,6,5′,6′-tetrahydro-β,β-carotin-5,5′-diol)Starting from our recently described synthon (+)-24, the enantiomerically pure 3,6:4,5:3′,6′:4′,5′-tetraepoxy-4,5,4′,5′-tetrahydro-ε,ε-carotene (34) and its 15,15′-didehydro analogue 32 were synthesized in eleven and nine steps, respectively (Scheme 4). Chiroptical data show, in contrast to the parent ε,ε-carotene, a very weak interaction between the chiral centers at C(5), C(5′), C(6), C(6′), and the polyene system. Diisobutylaluminium hydride reduction of 32 lead rather than to the expected 15,15′-didehydro analogue 35 of Cycloviolaxanthin (8), to the polyenyne 36 (Scheme 5). We explain this reaction by an oxirane rearrangement leading to a cyclopropyl ether followed by a fragmentation to an aldehyd on the one side and an enol ether on the other (Scheme 6). This complex rearrangement includes a shift of the whole polyenyne chain from C(6), C(6′) to C(5), C(5′) of the original molecule.
    Additional Material: 8 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19900730719
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  • 155
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    Kinetic and thermodynamic parameters for Schiff-rase formation between 5′-deoxypyridoxal and hexylamineSupported by the CICYT and the universidad de Alcalá de Henares (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 1991-1998 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The thermodynamic parameters involved in the formation of Schiff bases between 5′-deoxypyridoxal and hexylamine were determined at different pH values and a constant ionic strength (0.1 M). The overall and individual rale constants of formation and hydrolysis at 10, 15, 20, 25, and 30° were also determined. The enthalpy of the overall formation process was found to be negative at all the pH values assayed except the neutral, while its entropy was always positive. The results obtained show the great relevance of the phosphate group at C(5′) to the stabilization of the Schiff bases of pyridoxal 5′-phosphate.
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    URL: http://dx.doi.org/10.1002/hlca.19900730723
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  • 156
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    The Radical Anions of [2.2]Metaparacyclophane-1,9-diene and Some Derivatives: An ESR and ENDOR Study (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 2058-2069 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The radical anion of [2.2]metaparacyclophane-1,9-diene (1) has been fully characterized by its hyperfine data with the use of ESR, ENDOR, and TRIPLE-resonance spectroscopy. Assignments of all proton-coupling constants are based on comparison with the spectra of the radical anions of the 8-deuterio-, 1,2,9,10-tetradeuterio-, and 1,10,12,13,15,16-hexadeuterio derivative. The spin distribution in 1\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\scriptstyle {{\relbar}\kern-4pt {.} }} $\end{document} drastically differs from that in the radical anion of [2.2]metaparacyclophane (4), and it is not readily interpreted by semi-empirical MO-methods. The radical anions of 8-fluoro- (2) and 8-cyano[2.2]metaparacyclophane-1,9-diene (3) have also been investigated. Substitution of 1 by an F-atom in the ‘exposed’ 8-position, to yield 2, has only a minor effect on the π-spin distribution in the radical anion, as evidenced by the similar proton-hyperfine data for 1\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\scriptstyle {{\relbar}\kern-4pt {.} }} $\end{document} and 2\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\scriptstyle {{\relbar}\kern-4pt {.} }} $\end{document}. The 19F-coupling constant for 2\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\scriptstyle {{\relbar}\kern-4pt {.} }} $\end{document} is much smaller than expected, thus indicating a pronounced ‘ortho-effect’ in the pertinent position. The ESR and ENDOR spectra of 3\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\scriptstyle {{\relbar}\kern-4pt {.} }} $\end{document} in 1,2-dimethoxyethane (counterion K+) reveal an equilibrium between a tightly and a loosely ion-paired radical anion. Whereas the former is present exclusively in 2-methyltetrahydrofuran (K+), the latter prevails in N,N-dimethylformamide (Et4N+) and in mixtures of 1,2-dimethoxyethane with N,N′,N,N″,N,′N″-hexamethylphosphoric triamide (K+). The high temperatures required for the conformational flipping of the meta-bridged benzene ring in 1\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\scriptstyle {{\relbar}\kern-4pt {.} }} $\end{document}, 2\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\scriptstyle {{\relbar}\kern-4pt {.} }} $\end{document}, and 3\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\scriptstyle {{\relbar}\kern-4pt {.} }} $\end{document} to be fast on the hyperfine time-scale are well above the range appropriate for the studies of these radical anions.
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    URL: http://dx.doi.org/10.1002/hlca.19900730726
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  • 157
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    Synthesis of 24-Methylidene[24-14C]- and 24-Methylidene[7-3H]cholesterol (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 2097-2100 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The syntheses of 24-methylidene[24-14C]cholesterol (7a) and of 24-methylidene[7-3H]cholesterol (7b) from commercially available (20S)-3-oxopregn-4-ene-20-carbaldehyde (1) are described. The method also provides simple preparations of 3β-acetoxy[24-14C]chol-5-en-24-oic acid (4) and 24-oxocholest-5-en-3β-yl acetate (6b).
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  • 158
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    Carotinoide mit 7-Oxabicyclo[2.2.1]heptyl-Endgruppen. Teil II. Synthese von (2S,5R,6S,2′S,5′R,6′S)-2,5:2′5′-Diepoxy-5,6,5′,6′-tetrahydro-β,β-carotin (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 2190-2198 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Carotenoids mit 7-Oxabicyclo[2.2.1]heptyl-End Groups. Synthesis of (2S,5R,6S,2′S,5′R,6′S)-2,5:2′5′-Diepoxy-5,6,5′,6′-tetrahydro-β,β-caroteneMukayama's ester 6 (methyl (1S,2R,5S)-2,5-epoxy-2,6,6-trimethylcyclohexane-1-carboxylate) was transformed in a few conventional steps into the title compound 14. Its CD curve was found to be significantly different from that of the analogous 3,6-epoxide, a fact we tentatively lake as an indication of a (weak) electronic interaction between the ring O-atom and the π-orbitals of the polyene chain.
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    URL: http://dx.doi.org/10.1002/hlca.19900730816
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  • 159
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    The Solid-State and Solution Conformations of (+)-Chelidonine (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 2171-2178 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The solid-state and solution conformations of (+)-chelidonine (1), a biologically active alkaloid, were determined by X-ray diffraction and 1H-NMR spectroscopy, X-Ray diffraction analysis revealed a conformer with B/C ‘anti-type’ cis conjunction, a half-chair of ring B, and a twist half-chair of ring C. One H2O molecule per one alkaloid molecule was cocrystallized and stabilized by H-bonding with OH—C(11). Analysis of the thermal behavior of the crystal showed more thermal stability in the monohydrate than the anhydrate. The NMR measurement of concentration and temperature dependences in CDCl3 and in (CD3)2SO suggested that the OH group of 1 was intramolecularly H-bonded to N(5) in (CD3)2SO and intermolecularly H-bonded to the solvent in CDCl3. Conformational-energy calculations by the MNDO method showed that the intramolecular H-bond was little affected by the conformational stabilization of 1.
    Additional Material: 7 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19900730813
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  • 160
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    Novel Hydroxyicosatetraenoic and Hydroxyicosapentaenoic Acids and a 13-Oxo Analog. Isolation from a Mixture of the Calcareous Red Algae Lithothamnion corallioides and Lithothamnion calcareum of Brittany Waters (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 2183-2189 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A mixture of the red calcareous algae Lithothamnion corallioides CROUAN and Lithothamnion calcareum (PALLAS) ARESCHOUGH, from Brittany waters, gives, on ethanolic extraction, the novel icosanoids ethyl 13-hydroxy-arachidonate (=(+)-all-Z-ethyl 13-hydroxyicosa-5,8, 11,14,-tetraenoate; (+)-1)), ethyl 13-hydroxytimnodonate (=(+)-(all-Z)-ethyl 13-hydroxyicosa-5,8,11,14,17-pentaenoate ((+)-2), and (5Z,9E,11E,14E)-ethyl 8-hydroxy-13-oxoicosa-5,9,11,14-tetraenoate (3). Moreover, the ethyl esters of four known icosatetraenoic acids are contained in the above algae. Structural elucidations of these metabolites are based mainly on NMR data.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19900730815
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  • 161
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    Influence of the Axial Alkyl Ligand on the Reduction Potential of Alkylcob(III)alamins and Alkylcob(III)yrinates (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 2225-2241 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The irreversible-reduction potentials of 26 alkylcob(III)alamins (RCblIII 1a-z) and 26 alkylcob(III)yrinates (R‘Cby’III; 2a-z) (Ep 1a-z and Ep 2a-z, resp.) have been measured in situ by single-scan voltammetry of hydroxocob(III)alamin hydrochloride (vitamin B12b- HCl; 1) or heptamethyl cob(II)yrinate perchlorate (ClO4‘Cby’II; 2) in presence of the corresponding alkyl halides (RX;3a-z) in DMF. The reduction potentials of alkylcobalt complexes exhibiting half-life times as short as a few seconds become measurable by this technique. Thermodynamic cycles prove that the observed reduction potentials are closely related to the standard reduction potentials E°(R—CoIII + e-⇆R⋅ + CoI). Electron-withdrawing groups and/or an increased degree of substitution at the Co-bound C-atom in RCblIII and, R‘Cby’III shift Ep(1a-z) and Ep (2a-z) towards positive potentials. Linear correlations have been found between Ep(1a-z) (Ep(2a-z)) of RCblIII (R‘Cby’III) and the pKa of RH (or the Taft σ*- or the Hammett σp--values of R) within each class of R, i. e. MeCblIII (Me‘Cby’III), primary RCblIII (R‘Cby’III) and secondary RCblIII (R‘Cby’III). The correlations allow to distinguish between electronic effects of the Co-bound alkyl residues and their steric interactions with the corrin side chains. The correlations have further been used to visualize the light-induced formal insertion of an olefin into the Co, C-bond of an alkylcobalamin (Scheme 2, 1a→1u), a key step in the vitamin-B12-catalized C, C-bond formation.
    Additional Material: 7 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19900730820
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  • 162
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    Umsetzungen von 3-(Dimethylamino)-2,2-dimethyl-2H-azirin mit Barbitursäure-Derivaten (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 2275-2286 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reactions of 3-(Dimethylamino)-2,2-dimethyl-2H-azirines with Barbituric-Acid DerivativesThe reaction of 3-(dimethylamino)-2,2-dimethyl-2H-azirine (1) and 5,5-disubstituted barbituric acids 5 in i-PrOH at ca. 70° gives 2-[5-(dimethylamino)-4,4-dimethyl-4H-imidazol-2-yl]alkanamides of type 6 in good yields (Scheme 1). The formation of 6 proceeds with loss of CO2; various reaction mechanisms with a zwitterionic 1:1 adduct B as common intermediate are discussed (Schemes 2 and 5). Thermolysis of product 6 leads to 2-alkyl-5-(dimethylamino)-4,4-dimethyl-4H-imidazoles 8 or the tautomeric 2-alkylidene derivatives 8′ via elimination of HNCO (Scheme 3). The latter undergoes trimerization to give 1,3,5-triazine-2,4,6-trione. No reaction is observed with 1,5,5-trisubstituted barbiturates and 1 in refluxing i-PrOH, but an N-alkylation of the barbiturate occurs in the presence of morpholine (Scheme 4). This astonishing reaction is explained by a mechanism via formation of the 2-alkoxy-2-(dimethylamino )aziridinium ion H which undergoes ring opening to give the O-alkylated 2-amino-N1,N1-dimethylisobutyramide I as alkylating reagent (Scheme 4).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19900730824
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  • 163
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    Mitteilungen (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 2353-2353 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19900730826
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  • 164
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    Masthead (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990) 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19900730101
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  • 165
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    Synthesis of Peptides Containing α,α-Disubstituted α-Amino Acids by the Azirine/Oxazolone Method: The (12-20)-Nonapeptide of the Ionophore Alamethicin (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 13-24 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The (12-20)-nonapeptide Z-Leu-Aib-Pro-Val-Aib-Aib-Glu (OBzl)-Gln-Pheol (10) of the ionophor alamethicin was synthesized by a new strategy, using 3-amino-2,2-dimethyl-2H-azirines 2 as synthons for the α-aminoisobutyric acid (Aib) moieties.
    Additional Material: 1 Tab.
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    URL: http://dx.doi.org/10.1002/hlca.19900730103
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  • 166
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    Interaction between Oxygen Lone-Pair Orbitals of Ether and α,β-Unsaturated Ketone Functions in 3,5,6-Trimethylidene-7-oxabicyclo[2.2.1]heptan-2-one and 3,6-Dimethylidene-7-oxabicyclo[2.2.1]heptane-2,5-dione: A PE-Spectroscopic Investigation (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 1-12 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Controlled ozonolysis of 2,3,5,6-tetramethylidene-7-oxabicyclo[2.2.1]heptane (1) afforded 3,5,6-trimethylidene-7-oxabicyclo[2.2.1]heptan-2-one (2). Ozonolysis of 2 gave a 1:1 mixture of 3,5-dimethylidene-7-oxa-bicyclo[2.2.1]heptane-2,6-dione (3) and 3,6-dimethylidene-7-oxabicyclo[2.2.1]heptane-2,5-dione (4). The He(Iα) photoelectron (PE) spectra of 2 and 4 have been recorded. Comparison with the PE data of related systems, and with the result of ab initio STO-3G calculations, confirm the existence of significant through-bond interactions between the oxygen lone-pair orbitals n(CO) of the carbonyl functions and n(O) of the O(7) ether bridge.
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  • 167
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    1,2,3,4,4a,5,8,8a-Octahydro-4β,8aα-dimethylnaphthalen-4aβ-ol ( = Dehydrogeosmin), a Novel Compound Occurring in the Flower Scent of Various Species of cactaceae (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 133-139 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 1,2,3,4,4a,5,8,8a-octahydro-4β8aα-dimethylnaphthalen-4aβ-ol (= dehydrogeosmin; 1) has been identified as the olfactorily dominant compound in the flower scents of Rebutia marsoneri WERD., Dolichothele longimamma (DC.) BR. et R., and Sulcorebutia kruegeri (CARD.) RITT. The structure of 1, which might be of importance to the pollination biology of such Cactaceae, is based on spectral data and synthesis.
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    URL: http://dx.doi.org/10.1002/hlca.19900730114
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  • 168
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    Metal Complexes with Macrocyclic Ligands. Part XXXIIPart XXXI, see [1].. Reactivity studies of the pendant carboxylic group in a macrocyclic Cu2+ complex towards amide formation and its use as a protein-labelling agent (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 149-153 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The Cu2+ complex of 1, having a non-coordinating carboxylic group, can be reacted under the typical conditions of peptide formation with amines such as 2-methylpropylamine or (pyrid-2-yl)methylamine to give, after removal of Cu2+ with CN-, the amides 4 and 5. The Cu2+ ion is of paramount importance since it protects the four amino groups of the macrocycle so that the amide condensation can specifically be done with the exogenous amine It is also shown that the Cu2+ complex of 1 can be covalently attached to bovine serum albumin (BSA), thus opening the possibility to use this compound as a labelling agent for proteins and antibodies.
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    URL: http://dx.doi.org/10.1002/hlca.19900730116
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  • 169
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    Azomalonate Syntheses Part II. Synthesis and Reactivity of Novel 1,2,4-Triazin-5-one DerivativesPresented in part at the ‘XII European Colloquim on Heterocyclic Chemistry’, Reims France, September 1986 [1] (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 1700-1718 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Base treatment of azomalonates derived from N-substituted dialkyl (2-chloroacetamido)malonates results in the formation of 4-substituted alkyl 5-oxo-1,4,5,6-tetrahydro-1,2,4-triazine-3-carboxylates. The same malonates coupled with diazotized 2-amino-5-chlorobenzophenone or methyl anthranilate afford triazinones which can be cyclized into novel triazino[1,6-a]indoles. Two representative heterocycles are further characterized by typical reactions. Whereas oxidation gives the corresponding triazine-5,6-diones, the outcome of the reduction is strongly dependent on the nature of the substituent at C(4). Bromination followed by aqueous workup leads to the 6-hydroxy derivatives. Some mechanistic aspects of this novel triazinone synthesis are discussed.
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    URL: http://dx.doi.org/10.1002/hlca.19900730615
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  • 170
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    Stoffwechselprodukte von Mikroorganismen. 257. Mitteilung.256. Mitteilung: [1] (3S,5R,6E,8E)-Deca-6,8-dien-1,3,5-triol, ein neues Stoffwechselprodukt von Streptomyces fimbriatus (MILLARDet BURR 1926) (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 2129-2135 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: (3S,5R,6E,8E)-Deca-6,8-diene-1,3,5-triol, a New Metabolite from Streptomyces fimbriatus (MILLARD et BURR 1926)The title compound 2, a new C10-metabolite related to the previously found (3S-8E)-1,3-dihydroxydec-8-en-5-one (1), was isolated from the culture filtrate of Streptomyces fimbriatus, strain Tü 2335 by solvent extraction and chromatography. The constitution and the absolute configuration were determined by spectroscopic methods and chemical derivatization. The relative configurations were determined by NOE measurements with the silyl-protected 3,5-isopropylidene derivative of 2.
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    URL: http://dx.doi.org/10.1002/hlca.19900730808
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  • 171
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    Probing the Anomeric Effect in O—C—N Systems Theory vs. Experiment: MO-ab initio Calculations and a Structural-Statistical AnalysisStructure and Conformation of Heterocycles, Part 19. Part 18:[1a]Dedicated to Professor Jack D. Dunitz (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 2113-2128 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A combined computational (MO ab initio) and structural-statistical study of molecules containing the O—C—N moiety is presented. Aminomethanol, the simplest member of this series, was computed using GAUSSIAN-82 with the 3-21G and 6-31G* basis sets and with complete geometry optimization, as well as with MP3//6-31G*. A set of carefully selected molecules containing the O—C—N unit was retrieved from the Cambridge Structural Database (CSD), and its structural parameters were analyzed according to an established procedure. Comparison between experimental and computational data was thus made possible. Results are consistent with the co-existence of two unequal anomeric effects in this system: a strong nN-σ*C—O anomeric interaction, and a weak nπO-σ*C—N one. The ability of the two basis sets to reproduce the energies and structural characteristics of the stereoelectronic effects is assessed, including the significance of using polarization functions and the inclusion of correlation energy.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19900730807
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  • 172
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    Coenzyme F430 from Methanogenic Bacteria: Oxidation of F430 Pentamethyl Ester to the Ni(III) Form (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 2209-2217 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: F430M, the pentamethyl ester of coenzyme F430, can be oxidized reversibly by one electron. The oxidation potential has been determined, and the electrolytically prepared oxidation product was characterized by its UV/VIS and ESR spectrum. The strongly anisotropic and nearly axial ESR spectrum is consistent with a S = ½ species with the unpaired-electron spin density predominantly in a dz2-type orbital of the central nickel ion. The properties of Ni(III)F430M are discussed in the context of two hypothetical mechanisms for the catalytic role of coenzyme F430 in methyl coenzyme M reductase, which catalyses the last step of methane formation in methanogenic bacteria.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19900730818
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  • 173
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    Acyl Migration in d6 Iron Complexes (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 2251-2262 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The η2-acyl complex [Fe(η2-EtC=O)I (CO)(PEt3)2] (1a) reacts with phenylacetylene in refluxing Et2O to form a mixture of products including [Fe(C(Ph)=CHC(O)Et}I(CO)(PEt3)2] (3), [Fe{C(Ph)=CHC(O)Et}1(CO)2(PEt3)2] (4), and [Fe{C(=CHPh)C(O)Et)I(CO)(PEt3)2] (5). Compound 3 contains a ‘metallafurane’ unit, while 5 consists of a 4-member metallacycle. Compound 5 was characterized by X-ray crystallography. In contrast to 1a, the η2-acyl complex [Fe{η2-(i-Pr)CO}I(CO)(PEt3)2] (1b) reacts with phenylacetylene under similar conditions to produce [Fe{η2-C(O)C(Ph)=CH(i-Pr)}I(CO)(PEt3)2 (7) which was characterized spectroscopically. Modified extended Hückel theory calculations were made on the model compounds [Fe(η2-CHO)(CO)2(PH3)2]+ (14), [Fe(CHO)(HCCH)(CO)2(PH3)2]+ (15), [Fe(=C=CH2)(CHO)(CO)2(PH3)2]+ (16), [Fe{C(=CH2)CHO}(CO)2(PH3)2]+ (17), and {Fe(CH=CHCHO)(CO)2(PH3)2]+ (18). The calculations show that in the transformation 15→18, there exists a transition state lying 83.6 kJ/mol above the optimized geometry of 15 in which the formyl unit is rotated by 80° with respect to the Fe-acetylene plane. Conversion of 15 to 17 involves a [1,2]-H shift and an acyl-acetylene coupling reaction which probably occur synchronously.
    Additional Material: 6 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19900730822
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  • 174
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    The Coordination Chemistry of 1,2-Bis[(diphenylphosphino)methyl]benzene with Nickel(II), Palladium(II), Platinum(II), and Platinum(0) and the X-Ray Crystals Structure of [Pt{1,2-bis[(diphenylphospino)methyl]benzene}(C2H4)] (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 2263-2274 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The preparation of complexes [MX2(1)] (M = Ni, Pd, and Pi; X - Cl, Br, and I; 1 = 1,2-bis[(diphenylphosphino)methyl]benzene). [Pt(OSO2CH3)Et(1)], [Pt(alkene)(1)] (alkene - C2H2, and CH2 = CHCN), and [(1)Pt-(μ-H)2PtH(1)][BPh4] is reported. Their 1H- and 31P-NMR spectra were recorded and used lor structural assignments. The X-ray crystal structure of [Pt(C2H4)(1)] was determined. It is shown that the P—Pt—P bond angle in this complex differs significantly from those found in related compounds with monodentate phosphines, and that this difference is likely to be due to intramolecular contacts.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19900730823
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  • 175
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    Synthesis of Putative Intermediates on the Monensin Biosynthetic Pathway and Incorporation Experiments with the Monensin-Producing Organism (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 239-259 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: As a direct test of the Cane-Westley hypothesis concerning the mode of assembly of ether rings in the polyether class of ionophore antibiotics, we describe experiments culminating in the synthesis of three putative intermediates on the monensin biosynthetic pathway and incorporation experiments with these materials and the monensin-producing organism Streptomyces cinnamonensis. The putative intermediates synthesised include the trienes [21-3H]-7 and [13-3H]-10, and the diene [9-3H]-11. The results of the incorporation experiments conducted with whole cell cultures suggest that [13-3H]-10 and [21-3H]-7 are unable to cross the intact cell membrane of S. cinnamonensis, whereas diene [9-3H]-11 can gain entry to the cellular interior, but is then degraded efficiently, most likely by a pathway closely related to β-oxidation, without being specifically incorporated into the antibiotic.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19900730203
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  • 176
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    A New Catalytic System for the Hydroformylation of Styrene Using Alkene Complexes of Platinum(0) (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 284-287 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The platinum(0) complexes [Pt(C2H4)(PP)] (PP = 1,2-bis[(diphenylphosphino)methyl]benzene (2) and (+)-DIOP = (+)-1,4-bis(diphenylphosphino)-1,4-dideoxy-2,3-O-isopropyliden-D-threitol), when promoted by CH3SO3H, become active catalysts for styrene hydroformylation with total yields of aldehydes ranging from 44 to 67% und selectivities towards 3-phenylpropanal ranging from 80 to 88%. Smaller amounts of the corresponding alcohols (3-18%) are also obtained with a selectivity towards 3-phenylpropanol of 94-96%. When DIOP complexes were used, no stereoselectivity for asymmetric hydroformylation was observed.
    Additional Material: 1 Tab.
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    URL: http://dx.doi.org/10.1002/hlca.19900730207
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  • 177
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    Synthesis of 8-Aza-1,3-dideaza-2′-deoxyadenosine and 5,6-Disubstituted Benzotriazole 2′-Deoxy-β-D-Ribofuranosides via Nucleobase-Anion Glycosylation (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 316-325 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of 8-aza-1,3-dideaza-2′-deoxyadenosine (3a) as well as of 4- and 5,6-substituted benzotriazole 2′-deoxy-β-D-ribonucleosides is described (Schemes 1-3). Glycosylation of benzotriazole anions is stereoselective in all cases (exclusive β-D-anomer formation), but regioisomeric N1, N2, and N3-(2′-deoxyribofuranosides) are formed. The distribution of the regioisomers is controlled by the nucleobase substituents. Anomeric configuration as well as the position of glycosylation are determined by UV and NMR in combination with 1D-NOE-difference spectroscopy. The unprotonated forms of 4-aminobenzotriazoic 2′-deoxy-β-D-ribofuranosides 3a-c exhibit strong fluorescence.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19900730211
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  • 178
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    Über Pterin-Chemie 87. Mitteilung86. Mitteilung: [1].. Regiospezifische Synthese von (Polyhydroxypropyl)-pterinen: Herstellung von D-Anapterin und L-PrimapterinHerrn Prof. Dr. Wolfgang von Philipsborn mit den besten Wünschen zum 60. Geburtstag gewidmet (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 337-345 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Regiospecific Synthesis of (Polyhydroxypropyl)-pterins: Synthesis of D-Anapterin and L-PrimapterinCondensation of 2,5,6-triaminopyrimidin-4-one(5) with the semicarbazone of pentoses proceeds regiospecifically with formation of 7-(polyhydroxypropyl)pterins. D-Anapterin (=7-(D-erythro-1′,2′,3′-trihydroxypropyl)pterin; D-3) was obtained in 40% yield, and L-primapterin (=7-(L-erythro-1′,2′-dihydroxypropyl)pterin; L-4)in 10% yield.
    Additional Material: 5 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19900730213
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  • 179
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    Halochrome Moleküle 9. Mitteilung[1]. Substituierte 6,11-Dihydrospiro[[1]benzopyrano[4,3-b]indol-6,9′-9′H-xanthen]-2′,6′-diamine und ihre Aza-analogen: Neue Chromogene für schwarze Farbbilder (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 359-379 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Halochromic Molecules. Substituted 6,11-Dihydrospiro[[1]benzopyrano[4,3-b]indol-6,9′-9′H-xanthene]-2′,6′-diamines and Their Aza Analogues: New Chromogenes for Black Images.We have synthesized a series of substituted 6,11-dihydrospiro[[1]benzopyrano[4,3-b]indo1-6,9′-9′H-xanthene]-2′,6′-diamines and their respective aza analogues. These compounds develop a black colour in acidic media. The assumed structures of the analytically pure starting and final products are consistant with the fragmentations in the MS and are also supported by FT 1H-NMR. The UV/VIS spectra in buffered MeOH/H2O solutions were measured. From the ∊pH* curves, we determined the pK* values. The title compounds can be used in so-called pressure-sensitive copying systems.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19900730216
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  • 180
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    Umsetzung von 3-(Dimethylamino)-2H-azirinen mit 1,3-Oxazolidin-2-thion zu 3-(2-Hydroxyethyl)-2-thiohydantoinen (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 594-598 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reaction of 3-(Dimethylamino)-2H-azirines with 1,3-Oxazolidine-2-thione to 3-(2-Hydroxyethyl)-2- thiohydantoinsThe reaction of 3-(dimethylamino)-2H-azirines 1 and 1,3-oxazolidine-2-thione (6), in MeCN at room temperature, yields, after hydrolytic workup, 3-(2-hydroxyethyl)-2-thiohydantoins 7 (Scheme 2). In the case of the spirocyclic 1c, crystallization of the crude reaction mixture leads to spiro [cyclopentane-1, 7′(7′aH)-imidazo [4, 3-b] oxazole] -5′-thione 8c. The mechanism is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19900730307
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  • 181
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    Reaktionen von 3-(Dimethylamino)-2H-azirinen mit 1,3-Benzoxazol-2(3H)-thion (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 599-607 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reaction of 3-(Dimethylamino)-2H-azirines with 1,3-Benzoxazole-2(3H)-thioneThe reaction of 3-(dimethylamino)-2H-azirines 2 with 1,3-benzoxazole-2(3H)-thione (5), which can be considered as NH-acidic heterocycle (pKaca. 7.3), in MeCN at room temperature, leads to 3-(2-hydroxyphenyl)-2-thiohydantoins 6 and thiourea derivatives of type 7 (Scheme 2). A reaction mechanism for the formation of the products via the crucial zwitterionic intermediate A′ is suggested. This intermediate was trapped by methylation with Mel and hydrolysis to give 9 (Scheme 4). Under normal reaction conditions, A′ undergoes a ring opening to B which is hydrolyzed during workup to yield 6 or rearranges to give the thiourea 7. A reasonable intermediate of the latter transformation is the isothiocyanate E (Scheme 3) which also could be trapped by morpholine. In i-PrOH at 55-65° 2a and 5 react to yield a mixture of 6a, 2-(isopropylthio)-1,3-benzoxazole (12), and the thioamide 13 (Scheme 5). A mechanism for the surprising alkylation of 5 via the intermediate 2-amino-2-alkoxyaziridine Fis proposed. Again via an aziridine, e.g. H (Scheme 6), the formation of 13 can be explained.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19900730308
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  • 182
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    Stereoselectivity of Dienamine [4 + 2] Cycloadditions Synthesis of Functionalised Decalins and Drimanes (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 640-651 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The [4 + 2] cycloaddition stereoselectivity of dienamines 1-4 with dimethyl fumarate and fumaronitrile has been investigated, and functionalised decalins 21-40 have been prepared by elimination of Me2NH from cycloadducts 7-11 and 15-20; in the context of the synthesis of drimane sesquiterpenes, the reduction of dienediesters 29 and 30 is also described.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19900730313
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  • 183
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    Acid-Promoted Rearrangements of N-Substituted 8-Oxa-3-azatricyclo[3.2.1.02′4] octane-6,7-dicarboxylates: Remote Substituent Effects on the Regioselectivity of the N-Acylaziridine/Dihydrooxazone RearrangementThis work was presented in part at the autumn meeting of the Swiss Chemical Society, Bern, Oct. 21, 1988. (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 674-689 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Preparations of dimethyl (1RS,2SR,4RS,5SR,6SR,7RS)- and dimethyl (1 RS,2SR,4RS,5SR,6RS,7SR)-8-oxa-3-azatricyclo[3;2.1.024] octane-6,7-dicarboxylate 15 and18, resp.) and of their N-(tert-butyloxy)carbonyl (14, 17) and V-benzoyl (16, 19) derivatives are described. While treatment with nucleophilic acids (HCl, HBr. AcOH) of the exo, exo-diesters 14 and 16 gave the corresponding products 23-27 of aziridine trans -addition, the exo, endo -diesters 17 and 19 led to the corresponding amino-lactones 63 (methyl (1RS,2RS,3SR,6RS,7SR,9RS)-2-{[(tert-butyloxy)carbonyl] amino}-5-oxo-4,8-dioxatricyclo[4.2.1.0 37] nonane-9-carboxylate) and 64 (methyl (1RS,2RS,3SR,6RS,7SR,9SR)-2-(benzoylamino)-5-oxo-4,8-dioxatricyclo[4.2.1.0 3′7] (nonane-9-carboxylate). Under non-nucleophilic acidic conditions, the N-benzoylaziridine 16 was rearranged quantitatively into dimethyl (1RS,2SR,26SR,67SR,7SR,8SR,9SR)-4-phenyl-5,10-dioxa-3-azatricyclo[4.3.1.02′7] dec-3-ene-8,9-dicarboxylate(31), and 19 into dimethyl (1RS,2SR,26SR,67SR,7SR,8SR,9SR)-4-phenyl-3,10-dioxa-5-azatricyclo [5.2.1.02′6] dec-4-ene-8,9-di-carboxylate (65). Possible mechanisms of these highly selective reactions and rearrangements are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19900730316
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  • 184
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    Enantiomeric 3,7-Dimethylocta-1,7-dienes as Useful Chiral Building Blocks. A New Access to Both Optical Antipodes of Natural (E)-3,7-Dimethyloct-2-ene-1,8-diol and (E)-3,7-Dimethyloct-2-ene-1,8-dicarboxylic Acid (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 733-738 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ozonolysis of the easily available monoterpenoids (-)-1 and (+)-1 leads in high yield to the ketoaldehydes (-)-4 and (+)-4, which serve as convenient intermediates for efficient new routes to both optical antipodes of the naturally occurring octenediol (E)-2 (Monarch butterfly secretion product) and octene-dicarboxylic acid (E)-3 (Callosobruchus chinensis sex pheromone). All steps proceed with almost complete retention of configuration, ensuring the synthesis of the target compounds with high optical purity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19900730322
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  • 185
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    Mitteilungen (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 762-763 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19900730325
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  • 186
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    Tricyclic Pyridine Derivatives with High Affinity to the Central Benzodiazepine ReceptorDedicated to Dr. O. Isler on the occasion of his 80th birthday (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 763-781 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Novel tricyclic heterocycles were prepared and evaluated for their affinity to the central benzodiazepine receptor. The most potent compounds with IC50's in the nanomolar range were; found among thienoquinolizines and benzo[a]quinolizines (cf. Tables 2-5). The central ring of the tricyclic ring system may be partially unsaturated (cf. Tables 2 and 4) or fully unsaturated (cf. Tables 3 and 5) without loss of the high affinity to the receptor. The position of the ester group in the pyridinone ring is crucial for good binding (cf. Tables 1 and 2). It may be replaced by a broad variety of functional groups, e.g. amides, alkyl carbamates, alkyl groups, and hydroxyalkyl groups (cf. Tables 2-5). In the benzo[a]quinolizines, shifting the halogen atom from C(10) to C(9) leads to complete loss of affinity to the benzodiazepine receptor (cf. Table 4).
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    URL: http://dx.doi.org/10.1002/hlca.19900730402
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  • 187
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    Synthese von 2,4-Diamino-thieno[2,3-d]pyrimidin-DerivatenHerrn Dr. Otto Isler zum 80. Geburtstag gewidmet (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 797-803 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Synthesis of 2,4-Diamino-thieno[2,3-d]pyrimidinesCondensation of 2-aminothiophene-3-carbonitrile (4) with guanidine or sequential addition of CS2 and NH3 to 4 provides 2,4-diaminothieno[2,3-d]pyrimidine (7). This compound yields, after sequential addition of sec-BuLi and either [3-(trifluoromethyl)benzene]sulfenyl chloride (8) or the corresponding disulfide 9, followed by acidic work up, 2,4-diamino-6-{[3-(trifluoromethyl)phenyl]thio}thieno[2,3-d]pyrimidine (10). In another approach, 2-amino-5-{[3-(trifluoromethyl)phenyl]thio}thiophene-3-carbonitrile (11) obtained from 4 and 8 is transformed to 10 by condensation with guanidine. Corresponding to the second route, 2,4-diamino-6-[(naphth-2-yl)thio]thieno-[2,3-d]pyrimidine (16) is synthesized. Oxidation of 10 with m-chloroperbenzoic acid gives 2,4-diamino-6-{[3-(tri-fluoromethyl)phenyl]sulfinyl}thieno[2,3-d]pyrimidine (13).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19900730405
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  • 188
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    Pteridine. Teil XCIV1 Teil XCIII: [1].. Synthese und Eigenschaften von 5,6-Dihydro-6-(1,2,3-trihydroxypropyl)pteridinen: Kovalente intramolekulare Addukte (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 808-826 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Pteridines: Synthesis and Characteristics of 5,6-Dihydro-6-(1,2,3-trihydroxypropyl)pteridines: Covalent Intramolecular AdductsVarious 5,6-diaminopyrimidines (1, 15, 24, 33) were condensed with the phenylhydrazones of L-(2) and D-arabinose (3) in acidic medium under N2 to give formal 5,6-dihydro-6-(1,2,3-trihydroxypropyl)pteridines (see, e.g., 4 and 5), the latter turned out to exist preferentially as intramolecular adducts, the hexahydropyrano-[3,2-g]pteridines 6, 7, 16, 17, 25, 26, and 34, formed subsequently by addition of the terminal OH group of the side-chain to the C(7)=N(8) bond of the pteridine moiety. Spectroscopically, the isomeric hexahydrofuro-[3,2-g]pteridines 10,11,18,19, and 35 were also detected as minor components in the equilibrium mixtures. In the 4-amino-2-(methylthio)pteridine series, crystallization of 6 and 7 led to the stereochemically pure (3S,4R,4aR, 10aS)-6-amino-3,4,4a,5,10,10a-hexahydro-8-(methylthio)-2H-pyrano[3,2-g]pteridine-3,4-diol (8) and its corresponding enantiomer 9, respectively Structure 8 was proven by X-ray analysis. Acylation of the hexahydropyrano[3,2-g]pteridines yielded the more stable tri-, tetra-, and pentaacetyl derivatives 12-14, 20-23, 27-32, and 37-39 which were characterized and of which the absolute and relative configurations were determined (1H- and 13C-NMR and UV spectra, chiroptical measurements, elemental analyses).
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    URL: http://dx.doi.org/10.1002/hlca.19900730407
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  • 189
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    Technical Procedures for the Syntheses of Carotenoids and Related Compounds from 6-Oxo-isophorone: Syntheses of (3R,3′R)-Zeaxanthin. Part IDedicated to Dr. Otto Isler on the occasion of his 80th birthday (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 861-867 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Starting from the readily available, optically active (4R)-4-hydroxy-2,2,6-trimethylcyclohexanone (1), a new technical synthesis of (3R,3′R)-zeaxanthin is described. According to a 2(C9 + C6) + C10 = C40 construction scheme, the ketone 1 was first transformed with (E)-3-methylpent-2-en-4-yn-1-ol (5) into a C15-intermediate which, by a three-step sequence, could be converted into the known olefinic C15-Wittig salt 4. Optimized conditions for the final Wittig reaction of 4 with the C10-dialdehyde 3 are discussed. Based on 1, the overall yield of the entire technical process is ca. 40%.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19900730411
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  • 190
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    New 20(10→5)abeo-Diterpenoids from Pygmaeopremna herbacea (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 455-459 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Two new 20(10→5)abeo-abietune diterpenoids, pygmaeooins B (1) and C (2), have been isolated from the roots of Pygmaeopremna herbacea (Verbenaceae). Their structures were elucidated on the basis of spectroscopic data, and chemically, both compounds were correlated with each other. The absolute configurations were assigned tentatively on the basis of biogenetic pathway.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19900730225
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  • 191
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    Conformation Analysis of the 8-Membered Ring of 12H-Dibenzo [d, g] [1, 3, 2] dioxathiocines: Symmetric and Asymmetric Conformations (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 618-625 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 12H-dibenzo [d, g] dioxathiocines 2 and 4 are prepared by condensation of the corresponding bis[phenols] 1 and 3 with SOCl2 and SCl2, respectively. X-Ray analysis reveals the presence of the boat-chair (BC) form as the only conformer in the solid state of the cyclic thiodioxy derivative 4a, whereas the sulfinyldioxy compound 2a exists in the asymmetric axial boat (B) form, i. e. with endo (axial) orientation of the exocyclic O-atom. Conformational analysis using 1H-NMR spectroscopy indicates the presence of a boat form for compounds 2, whereas compounds 4 again exist in the boat chair form. A comparison of 1H-NMR and thermodynamic parameters with those of the cyclic sulfinyldioxy compound 5 with an equilibrium between e-BC and a-BC form (i.e. BC form with equatorial and axial orientation of the exocyclic O-atom) is made.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19900730310
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  • 192
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    Homogeneous and heterogeneous asymmetric reactions. Part 5Part 4, see [1]. Diastereoselective and enantioselective hydrogenation of cyclic β-keto esters on modified Raney-nickel catalysts (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 635-639 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The hydrogenations of methyl 2-oxoeyclopentanecarboxylate (1), ethyl 2-oxocyelohexanecarboxylate (3), and 2-methylcyclohexanone (5) on unmodified Raney-Ni catalyst lead predominately to the formation of the cis-hydroxy diastereoisomers of 2, 4, and 6, respectively (Scheme 2). In the asymmetric hydrogenations on catalysts modified with chiral tartaric acid ((R, R )-C4H6O6/Raney-Ni and (R, R)-C4H6O6/NaBr/Raney-Ni), the predominance of the cis-isomer increases significantly. The hydrogenations of β-keto esters 1 and 3 proceed with an enantioselectivity of 10-15% on the modified catalysts, while the similar hydrogenation of 5 yields optically inactive 6. The (1S,2R)-enantiomers of the cis-isomers of 2 and 4 are formed in larger quantity, whereas the (lR,2R)-enantiomers of the corresponding trans-isomers predominate (Scheme 1). The enantioselective formation of trans-2 and trans-4 can be interpreted mainly in terms of the asymmetric hydrogenation of cyclic β-keto esters through the keto form, while that of the corresponding cis-hydroxy esters proceeds through the enol form.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19900730312
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  • 193
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    Enantio- and Diastereoselective Aldol-Reaction of 2,6-Dimethylphenyl Propionate Using Titanium-Carbohydrate ComplexesPart 5 of ‘Enantioselective Syntheses with Titanium-Carbohydrate Complexes’ Part 4: [1d] (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 659-673 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Chloro(cyclopentadienyl)bis(1,2:5,6-di-O-isopropylidene-α-D-glucofuranos-3-O-yl)titanium (1) is used for the transmetallation of Li-enolates obtained from propionyl derivatives. While such Ti-enolates of ketones and hydrazones appear to be unreactive, the (E)enolate 13 of 2,6-dimethylphenyl propionate (11) adds to the re-side of aldehydes, affording various syn-aldols 14 with high dia- and enantioselectivity (92-97% ds, 91-97% ee, cf. Scheme 2 and Table 1). Racemic syn-aldols (±)-14 are obtained analogously from the achiral bis(2-propyloxy)-Ti-enolate 15 (Scheme 2 and Table 2). In contrast to the unstable Li-enolate 10, the Ti-enolates 13 and 15 isomerize at -30°, presumably to the thermodynamically more stable (Z)-enolates (Scheme 4), While the diastereoselectivity of the achiral enolate 15 is lost upon this equilibration, the chiral (Z)-enolate 27 quite unexpectedly affords anti-aldols 12 of high optical purity (94-98% ec) and, in most cases, with acceptable-to-good diastereoselectivity (82-90% ds). Notable exceptions are branched unsaturated and aromatic aldehydes which form a greater proportion of synepimers of moderate optical purity (Scheme 5 and Table 3). Consistent with these findings, re-facial-and ami -selective aldol-addition is also exhibited by the (Z)-configurated Ti-enolate 22 of N-propionyl-oxazolidi-none 19 (Scheme 3).
    Additional Material: 5 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19900730315
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  • 194
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    Synthese von enantiomerenreinen ‘Grasshopper’-Ketonen und verwandten Verbindungen (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 700-715 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Synthesis of Optically Pure Grasshopper Ketone and of Its Diastereoisomers and Related CompoundsStarting from our previously described synthon 1, the synthesis of four enantiomerically pure grasshopper ketons (diastereoisomeric 4-(2′,4′-dihydroxy-2′,6′,6′-trimethylcyclohexylidene)but-3-en-2-ons) and of their oxo derivatives was performed. Spectral and chiroptical data are presented.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19900730319
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  • 195
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    Synthesis, Structure, and 2D-NMR Studies of Novel Chiral (η3-Allyl)palladium(II) Complexes Containing the Bidentate Ligand Sparteine (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 723-732 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Novel cationic allylpalladium (II) comp, exes containing the alkaloid (-)sparteine (1) as a bidentate ligand have been prepared. Two of them, [η3(cyclohex-2-enyl)] (sparteine)palladium(II) hexafluorophosphate([Pd(η3-C6 H9)(sparteine)][PF6] 3b) and (sparteine)[η3-(1,1,3-triphenylallyl)] palladium (II) trifluorophosphate ([Pd(η3-Ph2CCHCHPh)(sparteine)][sparteine)] [CF3SO3]; (3c) were characterized by X-ray diffraction. The application of 2D-NMR methods (COSY and NOESY)affords a correlation between the solid-state and solution structures for complex 3c.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19900730321
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  • 196
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    Chiral [2H]-Labelled Methylene Groups in Trienoic- and Dienoic Fatty Acids: A Facile Approach via Asymmetric Epoxidation of [2H] Allyl Alcohols (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 754-761 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Chiral [2H] -labelled methylene groups flanked by two double bonds within (poly)unsaturated fatty acids are readily available from trans-2,3-epoxy[2,3-2H2] alk-4-yn-l-ols, obtained in their turn by asymmetric epoxidation of the corresponding (E)-[2,3-2H2] alk-2-en-4-yn-l-ols (see Scheme 3). The procedure is exemplified for (8S,3Z,6Z,9Z)-[7,8-2H2] trideca-3,6,9-trienoic acid ((8S)-11) and (8R)-11 (Scheme 4) as well as for (5S,3Z,6Z)-[4,5-2H2]deca-3,6-dienoic acid ((5S)-13) and (5R)-13 (Scheme 5).
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19900730324
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  • 197
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    Masthead (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990) 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19900730401
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  • 198
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    Chromatographische Trennung und quantitative Bestimmung aller acht Stereoisomeren von α-TocopherolHerrn Dr. Otto Isler zum 80. Geburtstag gewidmet (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 782-789 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Separation and Quantitation of All Eight Stereoisomers of α-Tocopherol by ChromatographyThe results of the analysis of several derivatives of (all-rac)-α-tocopherol by HPLC on a chiral stationary phase and by capillary GC on a achiral stationary phase are reported. Consecutive application of both methods to the ethyl-ether derivative allows the separation and quantification of all eight possible stereoisomers of (all-rac)-α-tocopherol.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19900730403
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  • 199
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    Coralloidolide F, the First Example of a 2,6-Cyclized Cembranolide: Isolation from the Mediterranean Alcyonacean Coral Alcyonium coralloidesThroughout this paper, we use the cembrene numbering for the structural formulae and spectroscopic data; IUPAC nomenclature and numbering are given in the Exper. Part. (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 804-807 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The Mediterranean alcyonacean Alcyonium ( = Parerythropodium) coralloides (Pallas, 1766) is shown here to contain coralloidolide F ( = (+)-(3a-R*, 7R*, 8R*, 9R*, 12R*, 12aS*)-8,9-epoxy-1,3a,6,7,8,9,10,11,12,12a-decahydro-3a-hydroxy-12-isopropenyl-2,5-dimethyl-1-oxocyclopfintacycloundecene-9,7-carbolactone; (+)-2), the first example of a 2,6-cyclized cembranolide. Structural assignments are mainly based on ID and 2D NMR and MS data.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19900730406
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  • 200
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    Photocycloaddition of Cyclohex-2-enones to Tetramethoxyethylene: Formation of 2,2,3,3-Tetramethoxy-1-oxaspiro[3.5]non-5-enesDedicated to Prof. Paul de Mayo on the occasion of his 65th birthday (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 856-860 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Cyclohex-2-enones 1a-1c undergo photocycloaddition to tetramethoxyethylene in benzene to afford 1-oxa-spiro[3.5]non-5-enes 3 in very good yields. In MeCN as solvent, higher relative amounts of bicyclo[4.2.0]octan-2-ones 4 are formed. Results from similar experiments with the same enones and 2,3-dimethylbut-2-ene or 1,1-dimethoxyethene indicate that the driving force for oxetane formation is a sufficiently large difference in redox potentials between Ered of the enone and Eox of the alkene. A mechanism is proposed for cycloalk-2-enone + alkene photocycloadditions wherein the cyclobutane adducts arise from an exciplex intermediate and the oxetanes from a subsequently formed contact ion-pair.
    Additional Material: 2 Tab.
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    URL: http://dx.doi.org/10.1002/hlca.19900730410
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